Fix check for branch enablement on event

When checking if an event is enabled for a specific branch, the wrong
name was being used. For example, branch "master" would fail when
checking against refPattern "refs/heads/master". Instead of using the
branch name, use the full refName to match.

Bug: issue 3099
Change-Id: I29a1b051e4cf7ddc944f0b1dc4111d81f8eb893e