Teach Commit Queue to handle changes that are in a non-default branch.
Teach Commit Queue to handle changes that are in a non-default branch.

This CL teaches the commit queue to handle changes to the kernel, and
any other repositories where the master branch name isn't 'master'.

BUG=chromium-os:21934
TEST=Confirm that commit queue now picks up changes by jrbarnette to
     kernel chromeos-2.6.38 branch, but doesn't pick up changes to
     other branches. Unit tests.

Change-Id: I16b7874b9fe96a840bff01fd30db65e984df1ada
Reviewed-on: http://gerrit.chromium.org/gerrit/10452
Reviewed-by: Chris Sosa <959d3d631fb6f17f1b07f751372041a1edb210d1@chromium.org>
Commit-Ready: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

coreos/chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite,coreos/chromite,coreos/chromite,chadversary/chromiumos.chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite