Externalize hooks for neutron functional jobs

Maintaining hook behavior in the config repo has the drawback of
being hard to test.  This change externalizes the hook definitions
for the neutron functional jobs so they can be maintained and
gated on via the neutron repo.

The supporting neutron change to master:

https://review.openstack.org/#/c/114717/

Change-Id: If5192cb22b5613c5ebcab63316c646ea3ab482df

modules/openstack_project/files/jenkins_job_builder/config/neutron-functional.yaml

@@ -24,15 +24,16 @@
               export OVERRIDE_ZUUL_BRANCH=$BRANCH_OVERRIDE
           fi
 
+          function gate_hook {{
+              bash -xe $BASE/new/neutron/neutron/tests/functional/contrib/gate_hook.sh
+          }}
+          export -f gate_hook
+
           function post_test_hook {{
-              $BASE/new/devstack/unstack.sh
-              cd $BASE/new/neutron
-              # Run tests as the stack user to allow sudo+rootwrap.
-              sudo chown -R stack:stack $BASE/new/neutron
-              echo "Running neutron functional test suite"
-              sudo -H -u stack tox -e dsvm-functional
+              bash -xe $BASE/new/neutron/neutron/tests/functional/contrib/post_test_hook.sh
           }}
           export -f post_test_hook
+
           cp devstack-gate/devstack-vm-gate-wrap.sh ./safe-devstack-vm-gate-wrap.sh
           ./safe-devstack-vm-gate-wrap.sh