Override constraints job to use proposal worker
Override constraints job to use proposal worker

Update the zuul parameter function so that the
propose-requirements-constraints-.* jobs run on
proposal.slave.openstack.org instead of the default bare-trusty
nodepool nodes.

Change-Id: I855ae0fce9fc8cb5efc1fc29ec354f8e0f7f8156

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