add infra-core to stable requirements
add infra-core to stable requirements

infra should have approve authority on requirements even on stable to
deal with pinning required for the gate.

Change-Id: If4b97a4d6f32c2ffeb55af3c4bf0627743f426a8

noorul/os-project-config,coolsvap/project-config,openstack-infra/project-config,noorul/os-project-config,citrix-openstack/project-config,anbangr/osci-project-config,open-switch/infra_project-config,dongwenjuan/project-config,citrix-openstack/project-config,Tesora/tesora-project-config,anbangr/osci-project-config,coolsvap/project-config,openstack-infra/project-config,dongwenjuan/project-config,Tesora/tesora-project-config,open-switch/infra_project-config