🌱 Ensure unhealthy machines get deletion priority

[fabriziopandini]

What this PR does / why we need it:
We recently merged #10712 under the assumption that when deleting machines on older MachineSets, unhealthy machines were prioritized.

This is only true for machines with NodeHealthy not set or false, but not for machines with HealthCheckSucceeded set to false by MHC.

This PR fixes this, and thus ongoing rollouts now contribute to a faster remediation of unhealthy machines.

/area machineset

cc @vincepri @enxebre @sbueringer

[enxebre]

Thanks!
/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 03466455e30cbdf85b9dd03a1d21b104caf50b68

[vincepri]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vincepri

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[sbueringer]

/hold

[sbueringer]

Let's please finish the discussion here: #10755 (comment)

It might be all good, but the reasoning atm is not correct.

[vincepri]

/cherry-pick release-1.7

[k8s-infra-cherrypick-robot]

@vincepri: new pull request created: #10761

In response to this:

/cherry-pick release-1.7

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