Add amphora update service client and API test

This patch adds a service client for the amphora agent configuration update
API and adds an API test for the amphora configuration update API.

It also adds the service client for amphora failover and cleans up some
client credintials in the amphora scenario tests.

Change-Id: I4b1a1f48d2f619b883619811539ddb262d6b5f45
diff --git a/octavia_tempest_plugin/tests/test_base.py b/octavia_tempest_plugin/tests/test_base.py
index 12929f4..2e46812 100644
--- a/octavia_tempest_plugin/tests/test_base.py
+++ b/octavia_tempest_plugin/tests/test_base.py
@@ -121,7 +121,7 @@
             cls.os_roles_lb_member.healthmonitor_client)
         cls.mem_l7policy_client = cls.os_roles_lb_member.l7policy_client
         cls.mem_l7rule_client = cls.os_roles_lb_member.l7rule_client
-        cls.mem_amphora_client = cls.os_roles_lb_member.amphora_client
+        cls.lb_admin_amphora_client = cls.os_roles_lb_admin.amphora_client
         cls.lb_admin_flavor_profile_client = (
             cls.os_roles_lb_admin.flavor_profile_client)
         cls.lb_admin_flavor_client = cls.os_roles_lb_admin.flavor_client