Add ability to detatch from running AzureVMCLuster and reconstruct the class later to refer to an existing cluster

The close() method deletes the cluster from Azure

But what if the user has done work on it and has saved work into the scheduler and wants to later come back and pick up where it stopped

It would be great if the user could stop the cluster which would stop all VMs but not delete them and that the user could later come back and restart the cluster by passing its ID