Add waiting OPERATION_STATUS for the third listener in tests.

This commit fixes the situation when test _test_listener_list fails
because of a mismatch OPERATION_STATUS. This error can be reproduced
only in really slow environments.

Change-Id: Ie873a59fffda425c60e912abbb0d3aec68e134ed
diff --git a/octavia_tempest_plugin/tests/api/v2/test_listener.py b/octavia_tempest_plugin/tests/api/v2/test_listener.py
index 152f6ff..2517a83 100644
--- a/octavia_tempest_plugin/tests/api/v2/test_listener.py
+++ b/octavia_tempest_plugin/tests/api/v2/test_listener.py
@@ -540,6 +540,11 @@
                 const.OPERATING_STATUS, const.ONLINE,
                 CONF.load_balancer.build_interval,
                 CONF.load_balancer.build_timeout)
+            listener3 = waiters.wait_for_status(
+                self.mem_listener_client.show_listener, listener3[const.ID],
+                const.OPERATING_STATUS, const.ONLINE,
+                CONF.load_balancer.build_interval,
+                CONF.load_balancer.build_timeout)
 
         # Test that a different users cannot see the lb_member listeners.
         expected_allowed = []