Port puppet-keystone-tripleo-standalone to os_tempest

Previously Tripleo validate-tempest role was used to run tempest
on tripleo jobs. Recently we are moving to os_tempest (an unified
role developed by openstack-ansible team).

It moves the vars to os_tempest. keystone tempest plugin is
installed by default so we donot need to keep tempest_services
var for the same.
Below is the other var changes:
run_tempest: false -> to disable validate-tempest role
use_os_tempest: true -> enable os_tempest
tempest_whitelist -> tempest_test_whitelist

Change-Id: I799d8634f4ed3d00346402c316a556c14c1b6d24
Signed-off-by: Chandan Kumar <chkumar@redhat.com>

.zuul.yaml

@@ -19,9 +19,8 @@
       TripleO standalone Job running Identity specific Tempest tests.
     vars:
       featureset_override:
-        run_tempest: true
-        tempest_whitelist:
+        run_tempest: false
+        tempest_test_whitelist:
           - 'identity'
           - 'keystone-tempest-plugin'
-        tempest_plugins:
-          - 'python-keystone-tests-tempest'
+        use_os_tempest: true