AS7-5070 - Invalid server-group name should fail start/stop/restart operations

AS7-5070 - Validation check for server-group name added to Start, Stop,
and Restart server-group operation handlers. Non-Existant server-group
name should result in failure with description: 

"JBAS014807: Management resource '[(\"server-group\" => \"<insert
server group name>\")]' not found"