Some bots should only run on the master branch

Bug: skia:6556
Change-Id: Iebe8b30de70685f56b795521ccc2242b0682000b
Reviewed-on: https://skia-review.googlesource.com/28660
Reviewed-by: Ben Wagner <benjaminwagner@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
2 files changed