check file exists before running osc functional tests

the stable/newton gate no longer works, and probably the
stable/mitaka and stable/liberty gates too.

see commit 1c1175a for
details about when the file was moved.

Change-Id: I780864751369c5d0a24a09b4c6a93a5af062fd62

jenkins/jobs/osc.yaml

@@ -27,8 +27,18 @@
           fi
           export DEVSTACK_LOCAL_CONFIG="enable_plugin neutron https://git.openstack.org/openstack/neutron"
           export ENABLED_SERVICES=q-qos
+
+          # NOTE(stevemar): After the newton release was tagged the file was moved.
+          # But, we run functional tests for various stable releases (liberty,
+          # mitaka, and newton).
+          # TODO(stevemar): Remove this check when Newton is EOL'ed.
+          hook_location=$BASE/new/python-openstackclient/openstackclient/tests/functional/post_test_hook.sh
+          if [ ! -f "$hook_location" ]; then
+            hook_location=$BASE/new/python-openstackclient/openstackclient/post_test_hook.sh
+          fi
+
           function post_test_hook {{
-              bash -xe $BASE/new/python-openstackclient/openstackclient/tests/functional/post_test_hook.sh
+              bash -xe $hook_location
           }}
           export -f post_test_hook