Logging improvements for clean shutdowns

Problem

There have been a few cases in the field where a user has raised a case asking why the node was failed over. Upon further investigation it turns out the node was cleanly shutdown by another administrator.  

Expectation

1. For the UI log to cleanly display that the node was asked to shutdown, this should be cluster wide
2. In diag.log there is a message saying "node X was asked to shutdown"
3. A failover caused by a clean shutdown needs to be explained. "Node X failed over because the node was cleanly shutdown without disabling auto failover"
4. The status in the UI should be 'Down - shutdown' (If we add support for sub states)