VisibleRefFilterIT: Add tests for tag visibility

These would have found the bug where we were using RefMap incorrectly.

The behavior is slightly non-obvious because of the way PushOneCommit
works. Rather than fight more with the acceptance test framework, just
document our expectations.

Change-Id: I0dcf80c84536cacdb216b93b2f36b0f6b680ce84
1 file changed