Add an active/standby scenario test

This patch adds a tempest scenario test for the active/standby topology.
It starts an active/standby load balancer, deletes the master amphora,
and validates that the load balancer is still working.

Change-Id: Ibcd5552a67cea650edc72bfaa986357267ca2407
diff --git a/octavia_tempest_plugin/config.py b/octavia_tempest_plugin/config.py
index 7c4ed2f..63c292b 100644
--- a/octavia_tempest_plugin/config.py
+++ b/octavia_tempest_plugin/config.py
@@ -66,7 +66,7 @@
                default=5,
                help='Interval to check for status changes.'),
     cfg.IntOpt('check_timeout',
-               default=60,
+               default=120,
                help='Timeout, in seconds, to wait for a status change.'),
     cfg.BoolOpt('test_with_noop',
                 default=False,