Fix owner_or_admin API tests

lb_observer and lb_global_observer don't have any meaning when
admin_or_owner policy override in enabled.
This commit disables client creation for those roles and removes their
uses from API tests (the behavior of the owner_or_admin tests are now
similar to their behavior before the introduction of the new RBAC
tests).

Requires the following configuration in tempest.conf:

[load_balancer]
RBAC_test_type = owner_or_admin
member_role = member
admin_role = admin

Change-Id: I2231384933d5974b962a558e8c0b3bffb1140b5a
diff --git a/octavia_tempest_plugin/tests/test_base.py b/octavia_tempest_plugin/tests/test_base.py
index e182d58..b9438e4 100644
--- a/octavia_tempest_plugin/tests/test_base.py
+++ b/octavia_tempest_plugin/tests/test_base.py
@@ -50,7 +50,12 @@
                            RBAC_tests.RBACTestsMixin, test.BaseTestCase):
     """Base class for load balancer tests."""
 
-    if CONF.load_balancer.enforce_new_defaults:
+    if CONF.load_balancer.RBAC_test_type == const.OWNERADMIN:
+        credentials = [
+            'admin', 'primary', ['lb_admin', CONF.load_balancer.admin_role],
+            ['lb_member', CONF.load_balancer.member_role],
+            ['lb_member2', CONF.load_balancer.member_role]]
+    elif CONF.load_balancer.enforce_new_defaults:
         credentials = [
             'admin', 'primary', ['lb_admin', CONF.load_balancer.admin_role],
             ['lb_observer', CONF.load_balancer.observer_role, 'reader'],