port test_extensions into nova v3 part2

this ports test_extensions into nova v3 and
corresponding extensions_client

Partially implements blueprint nova-v3-api-tests

Change-Id: Iebd57de78740e051505001a5c6dea91659c7e356
diff --git a/tempest/services/compute/v3/xml/extensions_client.py b/tempest/services/compute/v3/xml/extensions_client.py
index 1395b5a..e03251c 100644
--- a/tempest/services/compute/v3/xml/extensions_client.py
+++ b/tempest/services/compute/v3/xml/extensions_client.py
@@ -20,12 +20,12 @@
 from tempest.services.compute.xml.common import xml_to_json
 
 
-class ExtensionsClientXML(RestClientXML):
+class ExtensionsV3ClientXML(RestClientXML):
 
     def __init__(self, config, username, password, auth_url, tenant_name=None):
-        super(ExtensionsClientXML, self).__init__(config, username, password,
-                                                  auth_url, tenant_name)
-        self.service = self.config.compute.catalog_type
+        super(ExtensionsV3ClientXML, self).__init__(config, username, password,
+                                                    auth_url, tenant_name)
+        self.service = self.config.compute.catalog_v3_type
 
     def _parse_array(self, node):
         array = []