GUI-1050: Display the warning icon for empty security groups

https://eucalyptus.atlassian.net/browse/GUI-1050

Fixed the tile view to include the warning icon and create the link to the detail page
Verified the fix on AWS
@kyolee310: Note that you do not need to return None since Python will return None by default, although sometimes it helps to be explicit (--so feel free to leave it here).