Map flavor name not found Internal error to the ResourceExhausted MCM error code

[ririko-nakamura]

How to categorize this PR?

/area control-plane
/area auto-scaling
/kind enhancement
/platform openstack

What this PR does / why we need it:

From cluster-autoscaler's FAQ , machines that are not supported should be backed off.

This PR maps the flavor name not found Internal error to the MCM ResourceExhausted error code. This allows a machine type which is not supported on specified AZ can take the ResourceExhausted flow and backoff to other workergroups quicker.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Release note:

 Flavor name not found errors will be treated as ResourceExhausted errors and be backed off

[gardener-prow]

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This pull-request has been approved by: ririko-nakamura
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