lxd|kvm container provisioner fails on manual machines if model's cloud not available.

[Heather Lanigan]

A model was create with a cloud. All machines in the model are manual machines, which can create both kvm and lxd containers. However since the cloud no longer exists, both container provisioners are in a failure loop:

2024-01-23 16:48:02 ERROR juju.worker.dependency engine.go:695 "kvm-container-provisioner" manifold worker returned unexpected error: cannot load machine machine-5 from state: creating environ for model "model name" (a0b40c67-b7ee-43dd-878c-169dad81161e): authentication failed.: authentication failed
caused by: requesting token failed
caused by: failed executing the request http://x.x.0.132:5000/v2.0/tokens
caused by: Post "http://x.x.0.132:5000/v2.0/tokens": dial tcp x.x.0.132:5000: i/o timeout

It's not possible to change a models cloud after creation.

In theory the controller's cloud and credential definitions used by this model could be updated to point to a cloud which is alive to work around the issue.

Juju 2.9.44 and openstack cloud.