Set different hostname label for upcoming nodes

[liorfranko]

Function copying template node to use for upcoming nodes was
not chaning hostname label, meaning that features relying on
this label (ex. pod antiaffinity on hostname topology) would
treat all upcoming nodes as a single node.
This resulted in triggering too many scale-ups for pods
using such features. Analogous function in binpacking didn't
have the same bug (but it didn't set unique UID or pod names).
I extracted the functionality to a util function used in both
places to avoid the two functions getting out of sync again.

Which component this PR applies to?

Cluster Autoscaler

What type of PR is this?

/kind bug

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #
Charry pick #3883

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: liorfranko
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[liorfranko]

/assign @vivekbagade

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/lifecycle stale

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/close

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