storcon_cli: do not drain to undesirable nodes

[VladLazar]

Problem

The previous code would attempt to drain to unavailable or unschedulable nodes.

Summary of Changes

Remove such nodes from the list of nodes to fill.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

3210 tests run: 3068 passed, 0 failed, 142 skipped (full report)

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Flaky tests (1)

Postgres 15

• test_vm_bit_clear_on_heap_lock_blackbox: release

Code coverage* (full report)

• functions: 31.6% (6627 of 20989 functions)
• lines: 48.6% (51495 of 106042 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
6917ed0 at 2024-06-12T11:05:26.635Z :recycle:}

[arpad-m]

good catch, when I read that filter invocation I was wondering whether some duplication could be saved by unifying with a probably similar check below but by the time I came to the code below I forgot about the fact that this filtering is needed at all 😆