Fix Flatcar bug #11268 missing default value for ansible_interpreter_python_fallback variable

[oboudry-mvp]

What type of PR is this?

/kind bug

What this PR does / why we need it:
In some scenarios, a kubespray upgrade of a Flatcar based cluster fails with v2.25.0. This is due to the variable ansible_interpreter_python_fallback being referenced in file roles/bootstrap-os/tasks/flatcar.yml also this variable may not exist. This PR sets a default value of [] (empty list) in the case the ansible_interpreter_python_fallback variable does not exists.

Which issue(s) this PR fixes:

Fixes #11268

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: oboudry-mvp / name: Olivier Boudry (21b9589)

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[yankay]

/ok-to-test

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/lifecycle stale

[oboudry-mvp]

/remove-lifecycle stale

[VannTen]

/lgtm
/approve
/retest-failed

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: oboudry-mvp, VannTen

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[VannTen]

You need to rebase your branch, the CI setup has changed and the docker-machine executor is no longer available on the CI cluster

[oboudry-mvp]

Hi VannTen, If I'm not mistaken, it's been rebased.

[oboudry-mvp]

@VannTen not sure how to rebase my PR, I think I've made the error of amending the master branch, not a separate branch. Shall I recreate the PR or is there something I can do to fix it ?

[VannTen]

Oh you pushed on the master branch of your fork, I see what kind of problems you could have.
You could do somehting like that

$ git fetch <upstream-remote (github.com/kubernetes-sigs/kubespray)> # update the local copy of the main repo
$ git rebase upstream/master (from your branch) # replay your branch on top of upstream/master
$ git push --force # push to your fork's master

(It's generally a good idea to avoid using the 'master' branch from your fork for doing PRs, it's generally confusing.

[oboudry-mvp]

@VannTen Did the push with --force and it looks like it worked. Yes creating a branch would have been better. Thanks for your help!

[VannTen]

/lgtm
/retest-failed