Add ObjectStorageClient for cleanup

In object storage clients, there is a lot of duplicated code for
setting CONF. This patch adds ObjectStorageClient for removing them.

Change-Id: I07eb4af34b20ae94a09b6fa90ffeb3bc19e14762
diff --git a/tempest/services/object_storage/container_client.py b/tempest/services/object_storage/container_client.py
index 182c4d0..c55826b 100644
--- a/tempest/services/object_storage/container_client.py
+++ b/tempest/services/object_storage/container_client.py
@@ -17,20 +17,10 @@
 import urllib
 from xml.etree import ElementTree as etree
 
-from tempest.common import rest_client
-from tempest import config
-
-CONF = config.CONF
+from tempest.services.object_storage import base
 
 
-class ContainerClient(rest_client.RestClient):
-    def __init__(self, auth_provider):
-        super(ContainerClient, self).__init__(auth_provider)
-
-        # Overwrites json-specific header encoding in rest_client.RestClient
-        self.headers = {}
-        self.service = CONF.object_storage.catalog_type
-        self.format = 'json'
+class ContainerClient(base.ObjectStorageClient):
 
     def create_container(
             self, container_name,