frontend: identify user roles using enum values

Additional ActionGroups now returned by getUserActionGroups:

 CONSUME_QUOTA

ActionGroups that now are no longer returned by getUserActionGroups:

 CHANGE_VM_CUSTOM_PROPERTIES
 EDIT_ADMIN_VM_PROPERTIES
 EDIT_ADMIN_TEMPLATE_PROPERTIES

Change-Id: I2de0478fc80952c9a5816bd58a1d000df77a6681
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>