Checkout devstack-gate master in periodic jobs
Checkout devstack-gate master in periodic jobs

Periodic jobs don't have branch or ref set, so provide defaults
for those for the devstack-checkout (which now uses zuul-cloner
and therefore requires them).

Change-Id: I373b30de3e694ffe30b6b3819aaff6823777974e

anbangr/osci-project-config,anbangr/osci-project-config,noorul/os-project-config,noorul/os-project-config,Tesora/tesora-project-config,coolsvap/project-config,openstack-infra/project-config,coolsvap/project-config,dongwenjuan/project-config,dongwenjuan/project-config,Tesora/tesora-project-config,openstack-infra/project-config