CLOUDSTACK-4379: Reset VM states when host is removed from cluster

   If you shut down the agent while VMs are running, the management
server assumes that the VMs are continuing to run. You can then
delete the host while it is in 'disconnected' state, and those VMs
will be unusable, forever in running state. They can't change state
because the host no longer exists. This patch checks for any VMs
that may have been tied to the removed host and resets their state
so that cloudstack can continue to manage them.