skipping config tests that fail on Windows

Windows file locking throws errors on these tests.
using pytest.mark.xfail on unix socket test

This replaces the adjacent `_fails_on_windows`
variation of the `test_parse_network_address_unix_socket`
test, makes them one test, and simpler via the
annotation + xfail condition.
Merge pull request #328 from BigBlueHat/windows-test-skips

Skipping and expecting failure on Windows for some tests