Add iptables-based active/standby scenario test

This patch adds a tempest scenario test for active/standby topology.

This scenario takes a similar approach to scenario proposed in Change-Id
Ibcd5552a67cea650edc72bfaa986357267ca2407 with the difference that it
does not rely on amphora stats API. Instead, it uses iptables to log VIP
traffic and make assertions based on logging.

Co-Authored-By: Michael Johnson <johnsomor@gmail.com>

Change-Id: I24a6fc3387166ec6cdbd57a5ca9f63743748ec68
diff --git a/octavia_tempest_plugin/tests/test_base.py b/octavia_tempest_plugin/tests/test_base.py
index f8acc2b..6a9c12b 100644
--- a/octavia_tempest_plugin/tests/test_base.py
+++ b/octavia_tempest_plugin/tests/test_base.py
@@ -127,6 +127,7 @@
         cls.lb_admin_flavor_client = cls.os_roles_lb_admin.flavor_client
         cls.mem_flavor_client = cls.os_roles_lb_member.flavor_client
         cls.mem_provider_client = cls.os_roles_lb_member.provider_client
+        cls.os_admin_servers_client = cls.os_admin.servers_client
 
     @classmethod
     def resource_setup(cls):