Replace inheritance hierarchy with composition

In the process of unification of the clients code we should use
composition to allow easier replacement with common HTTPClient.

Related to blueprint common-client-library-2

Change-Id: I5addc38eb2e2dd0be91b566fda7c0d81787ffa75

glanceclient/v1/client.py

@@ -18,7 +18,7 @@ from glanceclient.v1 import images
 from glanceclient.v1 import image_members
 
 
-class Client(http.HTTPClient):
+class Client(object):
     """Client for the OpenStack Images v1 API.
 
     :param string endpoint: A user-supplied endpoint URL for the glance
@@ -30,6 +30,6 @@ class Client(http.HTTPClient):
 
     def __init__(self, *args, **kwargs):
         """Initialize a new client for the Images v1 API."""
-        super(Client, self).__init__(*args, **kwargs)
-        self.images = images.ImageManager(self)
-        self.image_members = image_members.ImageMemberManager(self)
+        self.http_client = http.HTTPClient(*args, **kwargs)
+        self.images = images.ImageManager(self.http_client)
+        self.image_members = image_members.ImageMemberManager(self.http_client)