scripts: sources-branch-updater-lib: Always fetch SHAs when working on master
scripts: sources-branch-updater-lib: Always fetch SHAs when working on master

When working on master, we should get the latest code from external
roles instead of the latest tag so ensure maximum compatibility with
the OSA code.

Change-Id: I83764ec2530537774cd7f130131a6628a697aaf9

openstack/openstack-ansible,bunchc/openstack-ansible,cfarquhar/openstack-ansible,openstack/openstack-ansible,yanyao/openstack-ansible,stackforge/os-ansible-deployment,stackforge/os-ansible-deployment,cfarquhar/openstack-ansible,bunchc/openstack-ansible,yanyao/openstack-ansible