Support skipping APP_COOKIE and HTTP_COOKIE

Not all provider drivers may support APP_COOKIE/HTTP_COOKIE,
so this patch modifies the test to reflect the same.

Change-Id: Ifea51c1f927947588ac2ed82f25fa35ee56c98f7
diff --git a/octavia_tempest_plugin/config.py b/octavia_tempest_plugin/config.py
index 11dc59f..ffc60ca 100644
--- a/octavia_tempest_plugin/config.py
+++ b/octavia_tempest_plugin/config.py
@@ -196,4 +196,8 @@
                default=False,
                help="Wether spare pool is available with amphora provider "
                     "driver or not."),
+    cfg.BoolOpt('session_persistence_enabled',
+                default=True,
+                help="Whether session persistence is supported with the "
+                     "provider driver."),
 ]