Ensure ostree variable has been defined

[electrocucaracha]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change

/kind bug

/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:
Apparently c942915 relies on the ostree variable definition, which for the runc container engine is not previously defined. This change ensures the variable is defined and fixes the error caused.

Which issue(s) this PR fixes:

Fixes #9161

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[cristicalin]

HI @electrocucaracha , please check and fix the commit message to make the bot happy.

/approve
/ok-to-test

[oomichi]

Nice work.

/lgtm

[floryut]

@electrocucaracha Thank you!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cristicalin, electrocucaracha, floryut

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[Jeroen0494]

@oomichi Could this PR please be backported to Kubespray 2.19 and 2.18? These are currently broken without this code for at least containerd on Ubuntu.

[2022-10-18T12:56:24.245Z] TASK [container-engine/runc : runc | set is_ostree] ****************************
[2022-10-18T12:56:24.245Z] Tuesday 18 October 2022  14:56:24 +0200 (0:00:00.121)       0:15:01.218 ******* 
[2022-10-18T12:56:24.245Z] fatal: [acc-jri-ot-k8sm001]: FAILED! => 
[2022-10-18T12:56:24.245Z]   msg: |-
[2022-10-18T12:56:24.245Z]     The task includes an option with an undefined variable. The error was: 'dict object' has no attribute 'stat'
[2022-10-18T12:56:24.245Z]   
[2022-10-18T12:56:24.245Z]     The error appears to be in '/var/lib/jenkins/workspace/k8s/08_docker_migrate_containerd/library/kubespray/roles/container-engine/runc/tasks/main.yml': line 2, column 3, but may
[2022-10-18T12:56:24.245Z]     be elsewhere in the file depending on the exact syntax problem.
[2022-10-18T12:56:24.245Z]   
[2022-10-18T12:56:24.245Z]     The offending line appears to be:
[2022-10-18T12:56:24.245Z]   
[2022-10-18T12:56:24.245Z]     ---
[2022-10-18T12:56:24.245Z]     - name: runc | set is_ostree
[2022-10-18T12:56:24.245Z]       ^ here