Previously with the config_files structure of config.json, the group
name was automatically set to the one of the user name. It is now
possible to set the group name in the same fashion than the
'permissions' structure with:
owner: 'desired_owner:desired_group'
Closes-Bug: #1696095
Change-Id: Ibae9f74e2351c81a717294467aedc51ea773c41e