User w/o group creation fix.

Fix exception when user is created w/o a group.
    
https://bugzilla.redhat.com/show_bug.cgi?id=1127093

@kbrock : looking at callers of ```rbac_edit_save_or_add``` there seems to be no place where user input might be passed in as ```what``` formal param.

But yes, a bit more of cleanup could be done, as the constant passed in is always a string that is then converted do symbol. Just plain unnecessary step.