trigger_parameterized_builds: Add support restrict-matrix-project.

When triggering a downstream matrix job, it can be useful to
restrict runs to a subset of all combinations. This is done
by a groovy filter, configured with the restrict-matrix-project
key.

Change-Id: I6ac252657e35c110f1caa48b59e970ed390935e5
Reviewed-on: https://review.openstack.org/35063
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Khai Do <zaro0508@gmail.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins