Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2018-06-11' into staging

Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2018-06-11' into staging

Block patches:
- Various bug fixes
- Removal of qemu-img convert's deprecated -s option
- qemu-io now exits with an error when a command failed

# gpg: Signature made Mon 11 Jun 2018 15:23:42 BST
# gpg:                using RSA key F407DB0061D5CF40
# gpg: Good signature from "Max Reitz <mreitz@redhat.com>"
# Primary key fingerprint: 91BE B60A 30DB 3E88 57D1  1829 F407 DB00 61D5 CF40

* remotes/maxreitz/tags/pull-block-2018-06-11: (29 commits)
  iotests: Add case for a corrupted inactive image
  qcow2: Do not mark inactive images corrupt
  block: Make bdrv_is_writable() public
  throttle: Fix crash on reopen
  block/qcow2-bitmap: fix free_bitmap_clusters
  qemu-img: Remove deprecated -s snapshot_id_or_name option
  iotests: Fix 219's timing
  iotests: improve pause_job
  iotests: Test post-backing convert target behavior
  qemu-img: Special post-backing convert handling
  iotests: Add test for rebasing with relative paths
  qemu-img: Resolve relative backing paths in rebase
  iotests: Let 216 make use of qemu-io's exit code
  iotests.py: Add qemu_io_silent
  qemu-io: Exit with error when a command failed
  qemu-io: Let command functions return error code
  qemu-io: Drop command functions' return values
  iotests: Repairing error during snapshot deletion
  qcow2: Repair OFLAG_COPIED when fixing leaks
  iotests: Rework 113
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>