Convert all service clients to global CONF object

This commit takes the rest client and all subclass(all the service
clients) and converts all uses of config to the global CONF object.

Partially implements bp config-cleanup

Change-Id: I09525af4f1b308b91d45b7bbea05e0f734ea485c
diff --git a/tempest/services/compute/xml/extensions_client.py b/tempest/services/compute/xml/extensions_client.py
index b2ab9da..98cd3e3 100644
--- a/tempest/services/compute/xml/extensions_client.py
+++ b/tempest/services/compute/xml/extensions_client.py
@@ -14,16 +14,20 @@
 #    under the License.
 
 from lxml import etree
+
 from tempest.common.rest_client import RestClientXML
+from tempest import config
 from tempest.services.compute.xml.common import xml_to_json
 
+CONF = config.CONF
+
 
 class ExtensionsClientXML(RestClientXML):
 
-    def __init__(self, config, username, password, auth_url, tenant_name=None):
-        super(ExtensionsClientXML, self).__init__(config, username, password,
+    def __init__(self, username, password, auth_url, tenant_name=None):
+        super(ExtensionsClientXML, self).__init__(username, password,
                                                   auth_url, tenant_name)
-        self.service = self.config.compute.catalog_type
+        self.service = CONF.compute.catalog_type
 
     def _parse_array(self, node):
         array = []