Added 2 user related testcases for Keystone V3API

This submission adds two test cases namely 'test_user_update' and
'test_list_user_projects' in script test_users.py. The suporting
methods are added to identity_client.py for JSON and XML calls.

Change-Id: I0a66b0c40bc275f4c0da3f57ea9c9d33cdeea455
Implements: blueprint keystone-v3-users-api-test
diff --git a/tempest/services/identity/xml/identity_client.py b/tempest/services/identity/xml/identity_client.py
index 6f1b1b3..99a155a 100644
--- a/tempest/services/identity/xml/identity_client.py
+++ b/tempest/services/identity/xml/identity_client.py
@@ -172,6 +172,12 @@
         body = self._parse_body(etree.fromstring(body))
         return resp, body
 
+    def get_user(self, user_id):
+        """GET a user."""
+        resp, body = self.get("users/%s" % user_id, self.headers)
+        body = self._parse_body(etree.fromstring(body))
+        return resp, body
+
     def delete_user(self, user_id):
         """Delete a user."""
         resp, body = self.delete("users/%s" % user_id, self.headers)