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/json/certificates_client.py b/tempest/services/compute/json/certificates_client.py
index f4d31ed..06e2ae7 100644
--- a/tempest/services/compute/json/certificates_client.py
+++ b/tempest/services/compute/json/certificates_client.py
@@ -16,15 +16,18 @@
 import json
 
 from tempest.common.rest_client import RestClient
+from tempest import config
+
+CONF = config.CONF
 
 
 class CertificatesClientJSON(RestClient):
 
-    def __init__(self, config, username, password, auth_url, tenant_name=None):
-        super(CertificatesClientJSON, self).__init__(config, username,
+    def __init__(self, username, password, auth_url, tenant_name=None):
+        super(CertificatesClientJSON, self).__init__(username,
                                                      password,
                                                      auth_url, tenant_name)
-        self.service = self.config.compute.catalog_type
+        self.service = CONF.compute.catalog_type
 
     def get_certificate(self, id):
         url = "os-certificates/%s" % (id)