Temporarily stop running tripleo seed/undercloud

* modules/openstack_project/files/zuul/layout.yaml: Until the
tripleo-ci cloud provider is back online and has nodepool nodes
again, these jobs are just going to be pending indefinitely. Don't
add new jobs for these nodes to the check pipeline for now until
they can be run again. Once the tripleo-ci cloud is back up and
working in nodepool, this can be safely reverted.

Change-Id: I0e06b7da92fe9875aab724d9ce421ef7361c81a4
Merge "Temporarily stop running tripleo seed/undercloud"