Description of problem:
The API returns different information for the following two calls:

* POST /api/v2/media
* GET /api/v2/media/:id

For POST the fields are:
[u'admin', u'created_at', u'id', u'updated_at', u'name']
FOR GET fields are:
[u'usergroups', u'name', u'roles', u'created_at', u'updated_at', u'external_usergroups', u'id', u'users']

So for POST, fields 'usergroups', 'roles', 'external_usergroups' and 'users' are missing.

Version-Release number of selected component (if applicable):
Sat6.1.6C5

How reproducible:
Always

Steps to Reproduce:
1. Create some UserGroup via API and investigate the server responce:
Making HTTP POST request to https://****************************.redhat.com:443/api/v2/usergroups with options {'verify': False, 'auth': ('admin', '********'), 'headers': {'content-type': 'application/json'}} and data {"usergroup": {"user_ids": [54], "role_ids": [23], "name": "testgroup"}}.

Actual results:
Received HTTP 201 response: {"admin":false,"created_at":"2016-01-25T15:22:37Z","id":3,"name":"testgroup","updated_at":"2016-01-25T15:22:37Z"}

Expected results:
Missing fields like 'users', 'roles', 'external_usergroups' and 'usergroups' should be present in server's response.

Additional info: