Fix merger handling of branches.

Force the creation of a remote tracking branch for every remote
branch on repo reset, and checkout the relevant branch before
applying each change.

Add tests that use multiple branches.

Change-Id: I5dbb22bc2eba829ffb9443889ebdf8ba573915c0
Reviewed-on: https://review.openstack.org/11566
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins
2 files changed