Switch to LVM thin provisioning

This change switches all LVM volumes being backed by a single thin
provisioning[1] pool.

This will allow day-2 operations to use spare physical space for
things such as:
- backups during a major upgrade on an ephemeral volume
- extending /srv or /var due to inaccurate storage capacity planning

This change enables the fstrim.timer unit on a daily schedule so that
the thin provisioning layer is notified of freed blocks.

[1] https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/9/html/configuring_and_managing_logical_volumes/creating-and-managing-thinly-provisioned-volumes_configuring-and-managing-logical-volumes

Change-Id: Id1c7e627b67b930347eed040176a9737cabc87d0
Depends-On: https://review.opendev.org/c/openstack/diskimage-builder/+/840144

elements/overcloud-partition-uefi/block-device-default.yaml

@@ -44,27 +44,46 @@
           base: [ "pv" ]
           options: [ "--force" ]
     lvs:
+        - name: lv_thinpool
+          type: thin-pool
+          base: vg
+          # 20MiB overhead from root partition size
+          size: 5044MiB
         - name: lv_root
+          type: thin
+          thin-pool: lv_thinpool
           base: vg
           # Volume sizes should be a multiple of 4MiB (1 LVM extent)
           # so this is rounded down from 3706MiB
           size: 3704MiB
         - name: lv_tmp
+          type: thin
+          thin-pool: lv_thinpool
           base: vg
           size: 240MiB
         - name: lv_var
+          type: thin
+          thin-pool: lv_thinpool
           base: vg
           size: 952MiB
         - name: lv_log
+          type: thin
+          thin-pool: lv_thinpool
           base: vg
           size: 240MiB
         - name: lv_audit
+          type: thin
+          thin-pool: lv_thinpool
           base: vg
           size: 192MiB
         - name: lv_home
+          type: thin
+          thin-pool: lv_thinpool
           base: vg
           size: 240MiB
         - name: lv_srv
+          type: thin
+          thin-pool: lv_thinpool
           base: vg
           size: 48MiB
 - mkfs:

elements/overcloud-partition-uefi/post-install.d/80-enable-fstrim

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+if [ "${DIB_DEBUG_TRACE:-0}" -gt 0 ]; then
+    set -x
+fi
+set -eu
+set -o pipefail
+
+sed -i "/^OnCalendar=/c\OnCalendar=daily" /usr/lib/systemd/system/fstrim.timer
+sed -i "/^Description=/c\Description=Discard unused blocks once a day" /usr/lib/systemd/system/fstrim.timer
+systemctl enable fstrim.timer