Reclaims the half-disk LV left by the Ubuntu Server autoinstall
template default. Idempotent — no-ops cleanly when there are no free PE
in the VG, and exits the play cleanly on hosts without LVM.
Supports ext4 and xfs. Does not handle partition resize (cloud-utils
growpart) — out of scope for the template fix-up case.
Wired into day1_deploy_honcho.yml ahead of the honcho role so newly
provisioned VMs get the fix-up automatically. Suitable to add to any
day1 playbook by simply listing it before the application role.
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