Only allow zuul user for infra-gate
Only allow zuul user for infra-gate

Do not allow a single +1 by jenkins to start the gate process, we should
require a +1 by zuul only.

Change-Id: I0808d27c139609cfce42f1e9d794cac94bb55cb5

openstack-infra/project-config,openstack-infra/project-config