Drop several Dracut modules and add boot.mount

[chewi]

It turns out huge chunks of our Dracut code have been obsolete for a while through systemd upgrades and switching to the minimal init.

This also drops sysroot-boot.service in favour of boot.mount. sysroot-boot.service used to be a simple mount unit way back before 8bf46fe. This was changed due to umount sometimes being called after an unmount had already happened, causing it and its associated unit to fail. This was harmless, but it did cause Kola test failures.

Although the precise cause of that issue was never found, I think that between moving the mount point outside of /sysroot, not forcing it to unmount before switching root (that will happen anyway), and the intervening 8 years of systemd changes, there's a good chance we won't see it again.

How to use

Just boot up, maybe with some provisioning.

Testing done

This Jenkins run has... I have also done a little manual testing.

• Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update) -- N/A
• Inspected CI output for image differences: /boot and /usr size, packages, list files for any missing binaries, kernel modules, config files, kernel modules, etc.

[Copilot]

Pull request overview

This PR removes several custom Dracut modules that are now obsolete due to systemd upgrades and the move to the minimal init flow, and replaces the initrd /sysroot/boot mounting logic (sysroot-boot.service) with a standard boot.mount unit that mounts the ESP at /boot during initrd when needed (e.g., for Ignition “first boot” quenching).

Changes:

• Replace sysroot-boot.service (+ retry-umount) with boot.mount, and update Ignition quenching to operate on /boot/... instead of /sysroot/boot/....
• Drop legacy/obsolete Dracut modules and associated generators/tests (usr generator, usr-fsck generator, verity generator, tmpfiles-early module).
• Adjust initrd unit ordering where needed (e.g., disk-uuid.service now orders before boot.mount), and update diskless generator to use ignition-remount-sysroot.service.

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test	Removes the top-level test runner script.
README.md	Removes documentation for running tests via ./test.
dracut/53ignition/sysroot-boot.service	Deletes the old initrd service that mounted the ESP at /sysroot/boot.
dracut/53ignition/retry-umount.sh	Deletes the retrying unmount helper previously used by sysroot-boot.service.
dracut/53ignition/module-setup.sh	Stops installing retry-umount/sysroot-boot.service; installs new boot.mount.
dracut/53ignition/ignition-remount-sysroot.service	Updates the Documentation URL.
dracut/53ignition/ignition-quench.service	Switches dependency to /boot and updates the quench path from /sysroot/boot to /boot.
dracut/53ignition/boot.mount	Adds a mount unit for the ESP at /boot in initrd.
dracut/53disk-uuid/disk-uuid.service	Updates ordering to run before boot.mount and ignition-disks.service.
dracut/52tmpfiles-early/systemd-tmpfiles-setup-dev-early.service	Deletes the custom early tmpfiles unit.
dracut/52tmpfiles-early/module-setup.sh	Deletes the module that installed the custom early tmpfiles unit.
dracut/51verity-generator/no-job-timeout.conf	Deletes verity-related drop-in used to disable job timeout.
dracut/51verity-generator/module-setup.sh	Deletes the verity generator module.
dracut/51usr-generator/usr-generator	Deletes the legacy usr= cmdline generator.
dracut/51usr-generator/testsuite.sh	Deletes the usr-generator tests.
dracut/51usr-generator/remount-sysroot.service	Deletes the legacy remount service used by the usr-generator flow.
dracut/51usr-generator/module-setup.sh	Deletes the usr-generator module setup/install logic.
dracut/51usr-fsck-generator/usr-fsck-generator	Deletes the generator that disabled fsck for /usr.
dracut/51usr-fsck-generator/testsuite.sh	Deletes the usr-fsck-generator tests.
dracut/51usr-fsck-generator/module-setup.sh	Deletes the usr-fsck-generator module setup/install logic.
dracut/51diskless-generator/module-setup.sh	Removes dependency on the deleted usr-generator module.
dracut/51diskless-generator/diskless-generator	Updates generated unit ordering to use ignition-remount-sysroot.service instead of remount-sysroot.service.

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