Output 'project' key in context's to_dict function

This adds the 'project' key to the output dict, which contains the same
value as the 'tenant' key.

Change-Id: I9f7514daa162c5a9f0e7c8c24455bd1d29517cf5

oslo_context/context.py

@@ -327,6 +327,7 @@ class RequestContext(object):
 
         return {'user': self.user_id,
                 'tenant': self.project_id,
+                'project': self.project_id,
                 'domain': self.domain_id,
                 'user_domain': self.user_domain_id,
                 'project_domain': self.project_domain_id,