Description of problem:

Any user can do a sustem shutdown as the command is not root level protected

Version-Release number of selected component (if applicable):

core4 / core5

How reproducible:

Issue shutdown command from general or guest user

Steps to Reproduce:
1.
2.
3.
  
Actual results:

System shuts down

Expected results:

Administrator password should be prompted for, if not root logon. That is,
shutdown should only be available from the root logon administration level. 

Additional info:
If the pc is behind a barrier, then the shutdown button is not available and the
system will not be able to suffer an unauthorized shutdown.