Fix response body format of orchestration_client to dict

'create_stack' function in orchestration_client return raw json strings.
However, in most of cases, raw json strings are not expected because it's
too hard to use. So we should do 'json.loads(body)' for the response body.
And the other apis such as {update,delete,suspend,resume} do not return a
response body in the API spec docs[1]. So we do not need to add
'json.load(body)' to the functions for now.

[1] http://developer.openstack.org/api-ref-orchestration-v1.html

Change-Id: Ic7d37d70aa0373d9bbf3ad302d1a521f5adaafe9

tempest/services/orchestration/json/orchestration_client.py

@@ -60,6 +60,7 @@ class OrchestrationClient(rest_client.RestClient):
         uri = 'stacks'
         resp, body = self.post(uri, headers=headers, body=body)
         self.expected_success(201, resp.status)
+        body = json.loads(body)
         return resp, body
 
     def update_stack(self, stack_identifier, name, disable_rollback=True,