Report tempest/devstack[-gate] merges to #openstack-dev.

Report merges to tempest, devstack, and devstack-gate to #openstack-dev
as these projects are in the same gate queue as the projects currently
reported to #openstack-dev. This should give us better IRC information
about the current state of the zuul queues.

Change-Id: I3822ca63fea84407d91037d1c8b77b405147f3fd
Reviewed-on: https://review.openstack.org/19832
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins