delete: Clean up machine directory if DeleteHost fails to

[tstromberg]

There are some situations where DeleteHost won't succeed. This outputs a warning, and tries to cleanup the directory anyways.

Old behavior with truncated config.json:

💣  Failed to delete cluster: Error getting migrated host: unexpected end of JSON input

😿  Sorry that minikube crashed. If this was unexpected, we would love to hear from you:
👉  https://github.com/kubernetes/minikube/issues/new/choose

New behavior with truncated config.json:

❌  Failed to delete cluster: load: filestore "minikube": Error getting migrated host: unexpected end of JSON input
📌  You may need to manually remove the "minikube" VM from your hypervisor
🔥  Removing /Users/tstromberg/.minikube/machines/minikube ...
💔  The "minikube" cluster has been deleted.

Closes #4286 and #5046

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[medyagh]

thanks for taking care of this.

I believe this was part of the delete all PR which has been wip for a while...#4780