Image Customizer: Fix special directories and partition customization.

[cwize1]

Merge Checklist

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

• The toolchain has been rebuilt successfully (or no changes were made to it)
• The toolchain/worker package manifests are up-to-date
• Any updated packages successfully build (or no packages were changed)
• Packages depending on static components modified in this PR (Golang, *-static subpackages, etc.) have had their Release tag incremented.
• Package tests (%check section) have been verified with RUN_CHECK=y for existing SPEC files, or added to new SPEC files
• All package sources are available
• cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json, .github/workflows/cgmanifest.json)
• LICENSE-MAP files are up-to-date (./SPECS/LICENSES-AND-NOTICES/data/licenses.json, ./SPECS/LICENSES-AND-NOTICES/LICENSES-MAP.md, ./SPECS/LICENSES-AND-NOTICES/LICENSE-EXCEPTIONS.PHOTON)
• All source files have up-to-date hashes in the *.signatures.json files
• sudo make go-tidy-all and sudo make go-test-coverage pass
• Documentation has been updated to match any changes to the build system
• Ready to merge

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Summary

Currently, the safechroot.Chroot class will auto-mount a bunch of the special directories (e.g. /dev, /proc, etc.). This is done (presumably) to permit more Linux utils to be runnable under the chroot.

However, when the image customizer tool is doing file-copy based partition customization, it has to make sure it avoids copying the contents of the special directories to avoiding messing up the host system. Currently, this is done by just explictly excluding the special directories from the copy operation. However, this can result in problems. For example, a directory not being created (e.g. /tmp) or a mount directory not receiving the correct extended attributes (e.g. SELinux).

This change adds an initialization option to safechroot.Chroot to set whether or not the special-directories are mounted. This allows the partition customization to do just a straight file-copy.

Change Log

• Image Customizer: Fix special directories and partition customization.

Does this affect the toolchain?

NO

Test Methodology

• Manually ran image customizer.
• Ran existing UTs.