TripleO: Reduce tempest test scope

This change reduces scope of tempest tests in tripleo job, so that we
run only subset of test cases used in TripleO repos.

Change-Id: If1ab96a8b78f47e3316c0a05b27f7827a27ab559
(cherry picked from commit 07d0fa7ab8)
(cherry picked from commit da08bab24c)

.zuul.yaml

@@ -23,6 +23,5 @@
       featureset_override:
         run_tempest: false
         tempest_test_whitelist:
-          - 'tempest.api.image'
           - 'tempest.scenario.test_server_basic_ops'
         use_os_tempest: true