Enable horizon in d-g job for django_os_auth

django_openstack_auth includes this devstack-gate job and relies on
horizon being enabled in devstack. Add a conditional check for this
specific project to the gate job.

Change-Id: I1e4a636bbe74d25ed45921b044298554ed0e8d2f

jenkins/jobs/devstack-gate.yaml

@@ -161,6 +161,9 @@
               export OVERRIDE_ZUUL_BRANCH=$BRANCH_OVERRIDE
           fi
           export DEVSTACK_PROJECT_FROM_GIT={name}
+          if [ "$DEVSTACK_PROJECT_FROM_GIT" == "django_openstack_auth" ] ; then
+              export DEVSTACK_GATE_HORIZON=1
+          fi
 
           # Even if the branch is overridden, make sure we use
           # the correct branch using the OVERRIDE_*_PROJECT_BRANCH