msc_vlr_tests: add CC Release test and test to catch OS#2779

These tests helped to debug issue OS#2779. Now that they're here we might as
well keep them.

The test test_call_mo_to_unknown shows that an MS answering to the Release
Request works as it should: the conn is torn down.

The test test_call_mo_to_unknown_timeout currently expects the error: the conn
remains active if the CC Release times out. This bug and the test expectations
will be fixed in I46ff2e9b09b67e4e0d79cccf8c04936f17281fcb.

Change-Id: Ic3c84520bff8c3fc82512d03ff6ab97d21b8fb7a
2 files changed