Switch to MiB for all partition/volume sizes

This change switches to MiB as the unit for all partitions and LVM
volumes. It includes comments stating overheads so any future changes
can be easily calculated.

All LVM MiB values are multiples of 4MiB, which is the size of an LVM
extent.

This change is in preparation for thin provisioning, where specifying
volume size by percentage no longer makes sense.

Change-Id: I768bb6def4fcea96a59357b4117d92efa3b9613b
Depends-On: https://review.opendev.org/c/openstack/diskimage-builder/+/839829

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

@@ -19,7 +19,7 @@
         size: 8MiB
       - name: boot
         type: 'BC13C2FF-59E6-4262-A352-B275FD6F7172'
-        size: 500MB
+        size: 500MiB
         mkfs:
           type: ext4
           mount:
@@ -29,7 +29,9 @@
               fsck-passno: 1
       - name: root
         flags: [ boot ]
-        size: 5500MB
+        # The passed-in DIB_IMAGE_SIZE is       6GiB, 6144MiB
+        # Otherwise, there is a 2MiB overhead
+        size: 5618MiB
 - lvm:
     name: lvm
     base: [ root ]
@@ -44,25 +46,27 @@
     lvs:
         - name: lv_root
           base: vg
-          extents: 69%VG
+          # Volume sizes should be a multiple of 4MiB (1 LVM extent)
+          # so this is rounded down from 3706MiB
+          size: 3704MiB
         - name: lv_tmp
           base: vg
-          extents: 4%VG
+          size: 240MiB
         - name: lv_var
           base: vg
-          extents: 15%VG
+          size: 952MiB
         - name: lv_log
           base: vg
-          extents: 4%VG
+          size: 240MiB
         - name: lv_audit
           base: vg
-          extents: 3%VG
+          size: 192MiB
         - name: lv_home
           base: vg
-          extents: 4%VG
+          size: 240MiB
         - name: lv_srv
           base: vg
-          extents: 1%VG
+          size: 48MiB
 - mkfs:
     name: fs_root
     base: lv_root