Implement simple mocking framework and test ntcr::StreamSocket shutdown sequence during connection phase using whitebox testing approach

[smtrfnv]

This PR brings an in-house lightweight framework to mock classes. The interface was inspired by existing mocking frameworks, though its current functionality is far behind from existing solutions. The main pro is that we do not introduce a dependancy to any new library.

This framework is used to test ntcr::StreamSocket shutdown sequence during connection phase.

[mattrm456]

OK to merge. I think we might run into potential problems with macros with simple, undecorated, all-uppercase names using like ONCE, TIMES, TO, etc. but let's tackle that when we notice that we are colliding with the preprocessor. And more generally, let's continue to integrate tests based upon this machinery to see where else we need to take this testing infrastructure.