Re-enable cross-vendor tests on Windows

[jacobperron]

There is a TODO regarding disabled cross-vendor tests on Windows:

system_tests/test_communication/CMakeLists.txt

Line 160 in f460b6e

# TODO(wjwwood): Connext and Fast-RTPS do not currently communicate over pub/sub

It would be nice to resolve these and have the tests re-enabled again. I'm not sure what's required to make these tests pass.

Here's an older related PR: #323
And an old issue that has been resolved: ros2/rmw_fastrtps#246

[jacobperron]

I've push a change re-enabling the tests (afa5184) and triggered a Windows build to see where we stand: