factory_diff: Look for remote branch with name starting with 'cros'.

BUG=None
TEST=Manually run factory_diff in my chroot with more two remotes
     and verify that remote branch is correctly located.

Change-Id: Iacbb5910877f0d53fc7399e8d6d4a489e0e813e9
Reviewed-on: https://chromium-review.googlesource.com/219471
Reviewed-by: Vic Yang <victoryang@chromium.org>
Tested-by: Ricky Liang <jcliang@chromium.org>
Commit-Queue: Ricky Liang <jcliang@chromium.org>
1 file changed