[net] Fix use of uninitialized value in getnetworkinfo(const JSONRPCRequest& request)

[net] Fix use of uninitialized value in getnetworkinfo(const JSONRPCRequest& request)

When running test_bitcoin under Valgrind I found the following issue:

```
$ valgrind src/test/test_bitcoin
...
==10465== Use of uninitialised value of size 8
==10465==    at 0x6D09B61: ??? (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21)
==10465==    by 0x6D0B1BB: std::ostreambuf_iterator<char, std::char_traits<char> > std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::_M_insert_int<unsigned long>(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, unsigned long) const (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21)
==10465==    by 0x6D0B36C: std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::do_put(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, unsigned long) const (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21)
==10465==    by 0x6D17699: std::ostream& std::ostream::_M_insert<unsigned long>(unsigned long) (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21)
==10465==    by 0x4CAAD7: operator<< (ostream:171)
==10465==    by 0x4CAAD7: formatValue<ServiceFlags> (tinyformat.h:345)
==10465==    by 0x4CAAD7: void tinyformat::detail::FormatArg::formatImpl<ServiceFlags>(std::ostream&, char const*, char const*, int, void const*) (tinyformat.h:523)
==10465==    by 0x1924D4: format (tinyformat.h:510)
==10465==    by 0x1924D4: tinyformat::detail::formatImpl(std::ostream&, char const*, tinyformat::detail::FormatArg const*, int) (tinyformat.h:803)
==10465==    by 0x553A55: vformat (tinyformat.h:947)
==10465==    by 0x553A55: format<ServiceFlags> (tinyformat.h:957)
==10465==    by 0x553A55: std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > tinyformat::format<ServiceFlags>(char const*, ServiceFlags const&) (tinyformat.h:966)
==10465==    by 0x54C952: getnetworkinfo(JSONRPCRequest const&) (net.cpp:462)
==10465==    by 0x28EDB5: CallRPC(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) (rpc_tests.cpp:31)
==10465==    by 0x293947: rpc_tests::rpc_togglenetwork::test_method() (rpc_tests.cpp:88)
==10465==    by 0x2950E5: rpc_tests::rpc_togglenetwork_invoker() (rpc_tests.cpp:84)
==10465==    by 0x182496: invoke<void (*)()> (callback.hpp:56)
==10465==    by 0x182496: boost::unit_test::ut_detail::callback0_impl_t<boost::unit_test::ut_detail::unused, void (*)()>::invoke() (callback.hpp:89)
...
```

The read of the uninitialized variable nLocalServices is triggered by g_connman->GetLocalServices()
in getnetworkinfo(const JSONRPCRequest& request) (net.cpp:462):

```c++
UniValue getnetworkinfo(const JSONRPCRequest& request)
{
...
    if(g_connman)
        obj.push_back(Pair("localservices", strprintf("%016x", g_connman->GetLocalServices())));
...
}
```

The reason for the uninitialized nLocalServices is that CConnman::Start(...) is not called
by the tests, and hence the initialization normally performed by CConnman::Start(...) is
not done.

This commit adds a method Init(const Options& connOptions) which is called by both the
constructor and CConnman::Start(...). This method initializes nLocalServices and the other
relevant values from the supplied Options object.