Merge #10711: [tests] Introduce TestNode

Merge #10711: [tests] Introduce TestNode

789733891 [tests] Introduce TestNode (John Newbery)

Pull request description:

  Continues #10082

  TestNode is a class responsible for all state related to a bitcoind node
  under test. It stores local state, is responsible for tracking the
  bitcoind process and delegates unrecognised messages to the RPC
  connection.

  This commit changes start_nodes and stop_nodes to start and stop the
  bitcoind nodes in parallel, making test setup and teardown much faster.

  On my vm, this changeset reduces total test_runner runtime for the base set of tests
  (including building the cache) from 263s to 195s (a 25% speedup). Note that the time
  reported by test_runner does not include time spent building the cache:

  *with TestNode*:
  ```
  → date +"%T" ; ./test_runner.py -q ; date +"%T"
  12:48:04
  ..................................................................................................................................................................................................................................................................................................................................
  TEST                           | STATUS    | DURATION

  abandonconflict.py             | ✓ Passed  | 12 s
  bip68-112-113-p2p.py           | ✓ Passed  | 19 s
  blockchain.py                  | ✓ Passed  | 8 s
  bumpfee.py                     | ✓ Passed  | 13 s
  decodescript.py                | ✓ Passed  | 3 s
  disablewallet.py               | ✓ Passed  | 3 s
  disconnect_ban.py              | ✓ Passed  | 6 s
  fundrawtransaction.py          | ✓ Passed  | 37 s
  getchaintips.py                | ✓ Passed  | 4 s
  httpbasics.py                  | ✓ Passed  | 3 s
  import-rescan.py               | ✓ Passed  | 4 s
  importmulti.py                 | ✓ Passed  | 6 s
  importprunedfunds.py           | ✓ Passed  | 3 s
  invalidblockrequest.py         | ✓ Passed  | 4 s
  invalidtxrequest.py            | ✓ Passed  | 4 s
  keypool.py                     | ✓ Passed  | 7 s
  listsinceblock.py              | ✓ Passed  | 4 s
  listtransactions.py            | ✓ Passed  | 33 s
  mempool_limit.py               | ✓ Passed  | 4 s
  mempool_persist.py             | ✓ Passed  | 15 s
  mempool_reorg.py               | ✓ Passed  | 4 s
  mempool_resurrect_test.py      | ✓ Passed  | 3 s
  mempool_spendcoinbase.py       | ✓ Passed  | 3 s
  merkle_blocks.py               | ✓ Passed  | 3 s
  multi_rpc.py                   | ✓ Passed  | 4 s
  net.py                         | ✓ Passed  | 3 s
  nulldummy.py                   | ✓ Passed  | 3 s
  p2p-compactblocks.py           | ✓ Passed  | 28 s
  p2p-fullblocktest.py           | ✓ Passed  | 126 s
  p2p-leaktests.py               | ✓ Passed  | 8 s
  p2p-mempool.py                 | ✓ Passed  | 3 s
  p2p-segwit.py                  | ✓ Passed  | 59 s
  p2p-versionbits-warning.py     | ✓ Passed  | 8 s
  preciousblock.py               | ✓ Passed  | 3 s
  prioritise_transaction.py      | ✓ Passed  | 5 s
  proxy_test.py                  | ✓ Passed  | 3 s
  rawtransactions.py             | ✓ Passed  | 9 s
  receivedby.py                  | ✓ Passed  | 19 s
  reindex.py                     | ✓ Passed  | 12 s
  rest.py                        | ✓ Passed  | 9 s
  rpcnamedargs.py                | ✓ Passed  | 3 s
  segwit.py                      | ✓ Passed  | 7 s
  sendheaders.py                 | ✓ Passed  | 24 s
  signmessages.py                | ✓ Passed  | 3 s
  signrawtransactions.py         | ✓ Passed  | 3 s
  txn_clone.py                   | ✓ Passed  | 4 s
  txn_doublespend.py --mineblock | ✓ Passed  | 4 s
  uptime.py                      | ✓ Passed  | 3 s
  wallet-accounts.py             | ✓ Passed  | 3 s
  wallet-dump.py                 | ✓ Passed  | 7 s
  wallet-encryption.py           | ✓ Passed  | 8 s
  wallet-hd.py                   | ✓ Passed  | 15 s
  wallet.py                      | ✓ Passed  | 31 s
  walletbackup.py                | ✓ Passed  | 104 s
  zapwallettxes.py               | ✓ Passed  | 9 s
  zmq_test.py                    | ○ Skipped | 0 s

  ALL                            | ✓ Passed  | 735 s (accumulated)
  Runtime: 189 s

  12:51:19
  ```

  *master*:
  ```
  → date +"%T" ; ./test_runner.py -q ; date +"%T"
  12:40:13
  ..........................................................................................................................................................................................................................................................................................................................................................................................................................................
  TEST                           | STATUS    | DURATION

  abandonconflict.py             | ✓ Passed  | 15 s
  bip68-112-113-p2p.py           | ✓ Passed  | 19 s
  blockchain.py                  | ✓ Passed  | 8 s
  bumpfee.py                     | ✓ Passed  | 20 s
  decodescript.py                | ✓ Passed  | 3 s
  disablewallet.py               | ✓ Passed  | 3 s
  disconnect_ban.py              | ✓ Passed  | 8 s
  fundrawtransaction.py          | ✓ Passed  | 36 s
  getchaintips.py                | ✓ Passed  | 11 s
  httpbasics.py                  | ✓ Passed  | 7 s
  import-rescan.py               | ✓ Passed  | 16 s
  importmulti.py                 | ✓ Passed  | 10 s
  importprunedfunds.py           | ✓ Passed  | 5 s
  invalidblockrequest.py         | ✓ Passed  | 4 s
  invalidtxrequest.py            | ✓ Passed  | 3 s
  keypool.py                     | ✓ Passed  | 7 s
  listsinceblock.py              | ✓ Passed  | 11 s
  listtransactions.py            | ✓ Passed  | 37 s
  mempool_limit.py               | ✓ Passed  | 4 s
  mempool_persist.py             | ✓ Passed  | 23 s
  mempool_reorg.py               | ✓ Passed  | 7 s
  mempool_resurrect_test.py      | ✓ Passed  | 3 s
  mempool_spendcoinbase.py       | ✓ Passed  | 3 s
  merkle_blocks.py               | ✓ Passed  | 10 s
  multi_rpc.py                   | ✓ Passed  | 6 s
  net.py                         | ✓ Passed  | 6 s
  nulldummy.py                   | ✓ Passed  | 3 s
  p2p-compactblocks.py           | ✓ Passed  | 30 s
  p2p-fullblocktest.py           | ✓ Passed  | 126 s
  p2p-leaktests.py               | ✓ Passed  | 8 s
  p2p-mempool.py                 | ✓ Passed  | 3 s
  p2p-segwit.py                  | ✓ Passed  | 62 s
  p2p-versionbits-warning.py     | ✓ Passed  | 8 s
  preciousblock.py               | ✓ Passed  | 8 s
  prioritise_transaction.py      | ✓ Passed  | 7 s
  proxy_test.py                  | ✓ Passed  | 10 s
  rawtransactions.py             | ✓ Passed  | 15 s
  receivedby.py                  | ✓ Passed  | 28 s
  reindex.py                     | ✓ Passed  | 12 s
  rest.py                        | ✓ Passed  | 12 s
  rpcnamedargs.py                | ✓ Passed  | 3 s
  segwit.py                      | ✓ Passed  | 12 s
  sendheaders.py                 | ✓ Passed  | 26 s
  signmessages.py                | ✓ Passed  | 3 s
  signrawtransactions.py         | ✓ Passed  | 3 s
  txn_clone.py                   | ✓ Passed  | 10 s
  txn_doublespend.py --mineblock | ✓ Passed  | 10 s
  uptime.py                      | ✓ Passed  | 3 s
  wallet-accounts.py             | ✓ Passed  | 3 s
  wallet-dump.py                 | ✓ Passed  | 6 s
  wallet-encryption.py           | ✓ Passed  | 8 s
  wallet-hd.py                   | ✓ Passed  | 18 s
  wallet.py                      | ✓ Passed  | 69 s
  walletbackup.py                | ✓ Passed  | 130 s
  zapwallettxes.py               | ✓ Passed  | 15 s
  zmq_test.py                    | ○ Skipped | 0 s

  ALL                            | ✓ Passed  | 936 s (accumulated)
  Runtime: 242 s

  12:44:36
  ```

Tree-SHA512: 6dfc4c11fd0caf7de6954c93679cf22c3df0acc6f432e616d1151062a61f456faa8ae2fe670b427868af55bb564802df84c8fd76e90b4b338750dbc23f46ad88