fallback_ips: ignore unreachable hosts

[poblahblahblah]

Sets ignore_unreachable: true to Gather ansible_default_ipv4 from all hosts task from fallback_ips.yml

Without this scale.yml will fail if a single node in the cluster is down, which for large clusters happens often.

Fixes #10313

What type of PR is this?

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/kind bug

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #10313

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

fallback_ips: ignore unreachable hosts

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[mzaian]

Thanks @poblahblahblah

/ok-to-test

[poblahblahblah]

@holmsten do you mind taking a look at this?

[floryut]

@poblahblahblah thanks for the PR
/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: floryut, mzaian, poblahblahblah

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[vishalc95]

From which release of kubespray , this fix will be available ?

[Rickkwa]

I tried cherry picking this change to 2.23.3 and I don't think it quite fixes it. While it doesn't error anymore, it also doesn't continue to the next task -- saying NO MORE HOSTS LEFT. Maybe an artifact of using run_once: true and it thinks the one host is unreachable, and thus doesn't continue to next tasks.