Description of problem:
Currently, when a server is removed from the database via the Admin UI -> Servers, the removed continues to run. The server will be fully operational for a while after the removal however operational integrity cannot be guaranteed. So far this functionality was intended to clear the database from previously decommissioned servers in an HA environment. It was not intended to remove servers that are still operational.

An enhancement was requested to shutdown the server if the server entity is removed from the database. 

Use case for enhancement:
1. Install at least one RHQ server
2. Go to Admin UI -> Servers 
3. Remove a server from the list of servers
4. The removed servers stops itself (on the next run of the internal heartbeat)

Notes:
1. The removal can be initiated from any server for any other server
2. The shutdown might not be immediate, as it will happen on the next heartbeat of the removed server.
3. The removed server will recreate the it's database entry if restarted later.
4. It is the user responsibility to properly decommission the server before or after this removal. 
5. The removal will only ensure that the server shutdown, it cannot prevent restarts (for example, if tied to system life-cycle) and thus getting the server fully operational.