Unable to decompose KVM pod

[Michael Iatrou]

Repro steps:

1. Using MAAS, deploy a physical machine.
2. Add the deployed machine as a KVM pod.
3. Compose a VM on the pod.
4. From the "Nodes" tab, release the physical machine.

Observed behavior:
Trying to delete the VM fails with:
The delete action for 1 node failed with error: Unable to decompose machine because: Failed talking to pod: Failed to login to virsh console.

The pod also cannot be decomposed:
Performing delete failed for 1 pod, see listing for specific error for each pod.
Unable to decompose machine because: Failed talking to pod: Failed to login to virsh console.

Expected behavior:
Have a way to clean up from this state.

maas 2.2.2-6099-g8751f91-0ubuntu1~16.04.1
maas-cli 2.2.2-6099-g8751f91-0ubuntu1~16.04.1
maas-common 2.2.2-6099-g8751f91-0ubuntu1~16.04.1
maas-dhcp 2.2.2-6099-g8751f91-0ubuntu1~16.04.1
maas-dns 2.2.2-6099-g8751f91-0ubuntu1~16.04.1
maas-proxy 2.2.2-6099-g8751f91-0ubuntu1~16.04.1
maas-rack-controller 2.2.2-6099-g8751f91-0ubuntu1~16.04.1
maas-region-api 2.2.2-6099-g8751f91-0ubuntu1~16.04.1
maas-region-controller 2.2.2-6099-g8751f91-0ubuntu1~16.04.1