OSModifier: Explicitly setting enforcing=0 for SELinux permissive mode

[elainezhao96]

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• [x] Ready to merge

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Summary

What does the PR accomplish, why was it needed? Found failure in trident pipeline deployments with permissive mode failed, while other deployments, this PR experiments explicitly setting enforcing=0 to ensure SELinux is in permissive mode from the very start of the boot process.

Does this affect the toolchain?

NO

Test Methodology

• Will publish new EMU and test in trident pipeline