Create api+scenario tests for listeners

This patch implements listener tests for the Octavia
Tempest Plugin.

Co-Authored-By: Adam Harwell <flux.adam@gmail.com>
Change-Id: I5c0d3a737ff4cc929573c6fb7fbb5d46f1159d80
Story: 2001387
Task: 5965
diff --git a/octavia_tempest_plugin/clients.py b/octavia_tempest_plugin/clients.py
index aa1949f..396fa7d 100644
--- a/octavia_tempest_plugin/clients.py
+++ b/octavia_tempest_plugin/clients.py
@@ -16,6 +16,8 @@
 from tempest import config
 
 from octavia_tempest_plugin.services.load_balancer.v2 import (
+    listener_client)
+from octavia_tempest_plugin.services.load_balancer.v2 import (
     loadbalancer_client)
 
 CONF = config.CONF
@@ -29,3 +31,5 @@
 
         self.loadbalancer_client = loadbalancer_client.LoadbalancerClient(
             self.auth_provider, SERVICE_TYPE, CONF.identity.region)
+        self.listener_client = listener_client.ListenerClient(
+            self.auth_provider, SERVICE_TYPE, CONF.identity.region)