Add tld_client's methods and tests to Designate tempest plugin

Partially-Implements: blueprint designate-tempest-plugin

Change-Id: Ic23a9249d0cf5c34e5c2c083b465200fa6c5da66
diff --git a/designate_tempest_plugin/clients.py b/designate_tempest_plugin/clients.py
index 5edc75a..9e64b15 100644
--- a/designate_tempest_plugin/clients.py
+++ b/designate_tempest_plugin/clients.py
@@ -28,6 +28,8 @@
     RecordsetClient
 from designate_tempest_plugin.services.dns.v2.json.pool_client import \
     PoolClient
+from designate_tempest_plugin.services.dns.v2.json.tld_client import \
+    TldClient
 
 CONF = config.CONF
 
@@ -56,3 +58,5 @@
                                                 **params)
         self.pool_client = PoolClient(self.auth_provider,
                                       **params)
+        self.tld_client = TldClient(self.auth_provider,
+                                    **params)