proxy: Fix the no_proxy variable

[VannTen]

What type of PR is this?
/kind bug

What this PR does / why we need it:
#12872 causes the no_proxy variable is rendered as an array of character rather than a string. (weird interaction between the manual jinja templating and the select ?)

This results in broken cluster in some case.

Eliminate the custom jinja looping to use filters and list flatteing +
join instead.
Also simplify some things (no separate tasks file, just use run_once
instead of delegating to localhost)

Which issue(s) this PR fixes:
Fixes #12977

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Fix broken NO_PROXY variable

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: VannTen

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[VannTen]

/cherrypick release-2.30
/cherrypick release-2.29

[k8s-infra-cherrypick-robot]

@VannTen: once the present PR merges, I will cherry-pick it on top of release-2.29, release-2.30 in new PRs and assign them to you.

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In response to this:

/cherrypick release-2.30
/cherrypick release-2.29

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[VannTen]

/cc @tico88612

[VannTen]

/hold

[VannTen]

/hold cancel

[tico88612]

@1337andre could you verify this one?

[VannTen]

Ugh, from a quick grep in bootstrap_os we don't add no_proxy to package management config (why ?) so the check with and invalid proxy server is not gonna work 🤔

(the fix did work for our clusters with a proxy but I need to think on how to add a regression test which does not need a real proxy server 🤔 )

[VannTen]

Looks like ansible 2.18 is more strict on allowing transient undefined ? I think <undefined val>.key in a list then filtering by undefined worked before ... 🤔 Oh well.

[VannTen]

That variable will disappear in #12897 anyway.

[VannTen]

/cc @tico88612