New scenario test case for TLD + re-factoring

1) Moving "test_create_zone_for_not_existing_tld" from API
   to scenario: "test_create_zone_using_not_existing_tld"
   Create a Zone using not existing TLD is supposed to FAIL
2) New test case: "test_create_zone_using_existing_tld"
   Create a Zone using existing TLD is supposed to PASS
3) Using indexes instead of underscores variables
4) Adding "tld_suffix" parameter into configuration (default is: 'com')
   to avoid (Non existing TLD) issues. All tests will be using
   the same(common) TLD suffix.

Change-Id: Ie9fca2598a3eab66f9cbd718e52e575744def160
diff --git a/designate_tempest_plugin/config.py b/designate_tempest_plugin/config.py
index 99c9a04..759903e 100644
--- a/designate_tempest_plugin/config.py
+++ b/designate_tempest_plugin/config.py
@@ -51,8 +51,10 @@
                help="The timeout on a single dns query to a nameserver"),
     cfg.StrOpt('zone_id',
                help="The target zone to test the dns recordsets "
-                    "If it is not specified, a new zone will be created ")
-
+                    "If it is not specified, a new zone will be created "),
+    cfg.StrOpt('tld_suffix',
+               default='com',
+               help="TLD suffix that used in all tests (if not overridden)")
 ]
 
 dns_feature_group = cfg.OptGroup(name='dns_feature_enabled',