Fix hard-coded master branch
Fix hard-coded master branch

Now that we have a configurable "source branch", we need to use
that branch when creating the list of commits to process.

Change-Id: Iec940d75e56e2ceccafe8e4c3bf437fed46c73d9

openstack-packages/DLRN,openstack-packages/delorean,openstack-packages/DLRN,openstack-packages/delorean