Add 'user' field to reservation requests

Change-Id: I34594aeaf4ef03fbeb10f50faf2d6824437d32cc
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1289
Reviewed-by: Henry Robinson <henry@cloudera.com>
Tested-by: Henry Robinson <henry@cloudera.com>
(cherry picked from commit 7cc19a36a6435c35cbd8c7f1c95449fed4f0494f)
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1291
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1321
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins