New API test - test_list_service_statuses

Test scenario:
  Initiate "Service Statuses" API request and make sure that:
  1) All mandatory services are listed in API responce
  2) Each listed service is in "UP" status

Change-Id: Ib11297d5e17df8caf9e8b533c3dccdbe97899dec
diff --git a/designate_tempest_plugin/clients.py b/designate_tempest_plugin/clients.py
index 87b43c4..43ec5a7 100644
--- a/designate_tempest_plugin/clients.py
+++ b/designate_tempest_plugin/clients.py
@@ -47,6 +47,8 @@
     import TransferAcceptClient
 from designate_tempest_plugin.services.dns.v2.json.tsigkey_client \
     import TsigkeyClient
+from designate_tempest_plugin.services.dns.v2.json.service_client \
+    import SevriceClient
 
 CONF = config.CONF
 
@@ -93,6 +95,7 @@
         self.transfer_request_client = TransferRequestClient(**params)
         self.transfer_accept_client = TransferAcceptClient(**params)
         self.tsigkey_client = TsigkeyClient(**params)
+        self.service_client = SevriceClient(**params)
 
         self.query_client = QueryClient(
             nameservers=CONF.dns.nameservers,