Use cirros image for overcloud testing

There is no need to build a fully operational image for testing
the overcloud in TripleO. A simple cirros image, with a smaller
memory and disk footprint and with no need to be built using dib
will accelerate the testing.

Change-Id: Iafac7ca4f18fd4734ae242242f73395ecbae80d6

modules/openstack_project/files/jenkins_job_builder/config/tripleo.yaml

@@ -149,6 +149,7 @@
           export USE_IRONIC=0
           sudo chown -hR $(whoami) /opt/git
           export OVERCLOUD_CONTROLSCALE=1
+          export USE_CIRROS=1
           function gate_hook {
               bash -xe /opt/stack/new/tripleo-ci/toci_gate_test.sh
           }
@@ -192,6 +193,7 @@
           export TRIPLEO_TEST=overcloud
           export OVERCLOUD_CONTROLSCALE=3
           export USE_IRONIC=1
+          export USE_CIRROS=1
           function gate_hook {
               bash -xe /opt/stack/new/tripleo-ci/toci_gate_test.sh
           }