Cannot delete a machine if there is no cluster

[chuckha]

/kind bug

What steps did you take and what happened:
I created a cluster and then a machine and deleted them both. The cluster was deleted and then the machine was unable to delete because it couldn't find the cluster:

E0801 14:08:10.060421       1 controller.go:218] controller-runtime/controller "msg"="Reconciler error" "error"="failed to get cluster \"my-cluster\" for machine \"my-machine\" in namespace           
\"default\": Cluster.cluster.x-k8s.io \"my-cluster\" not found"  "controller"="machine-controller" "request"={"Namespace":"default","Name":"my-machine"}                                                

What did you expect to happen:
I expect the machine to be deleted.

[ncdc]

/assign
/lifecycle active

[ncdc]

I'm going to port #1180 to master to fix this