TT#118659 Ensure that wiping disk signatures works more reliably

Noticed while debugging the EFI situation, that wipefs calls might fail, like:

| # wipefs -a /dev/nvme0n1
| wipefs: error: /dev/nvme0n1: probing initialization failed: Device or resource busy

Using the force option, we *could* get past this error:

| # wipefs -af /dev/nvme0n1
| /dev/nvme0n1: 8 bytes were erased at offset 0x00000200 (gpt): 45 46 49 20 50 41 52 54
| /dev/nvme0n1: 8 bytes were erased at offset 0x3a38b2de00 (gpt): 45 46 49 20 50 41 52 54
| /dev/nvme0n1: 2 bytes were erased at offset 0x000001fe (PMBR): 55 aa

But quoting from wipe2fs(8):

| -f, --force
|        Force erasure, even if the filesystem is mounted.  This is required in order to erase a partition-table signature on a block device.

So while this would work, there might be unexpected side effects.
Instead let's use a different approach: if we remove the LVM signatures
*before* running wipefs, it behaves as expected:

| root@grml ~ # pvs
|   PV             VG   Fmt  Attr PSize    PFree
|   /dev/nvme0n1p3 ngcp lvm2 a--  <232.41g <222.41g
| root@grml ~ # vgs
|   VG   #PV #LV #SN Attr   VSize    VFree
|   ngcp   1   1   0 wz--n- <232.41g <222.41g
| root@grml ~ # lvs
|   LV   VG   Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
|   root ngcp -wi-a----- 10.00g
| root@grml ~ # wipefs -a /dev/nvme0n1
| wipefs: error: /dev/nvme0n1: probing initialization failed: Device or resource busy
| 1 root@grml ~ # vgremove -ff ngcp
|   Logical volume "root" successfully removed
|   Volume group "ngcp" successfully removed
| root@grml ~ # pvremove /dev/nvme0n1p3 --force --force --yes
|   Labels on physical volume "/dev/nvme0n1p3" successfully wiped.
| root@grml ~ # wipefs -a /dev/nvme0n1
| /dev/nvme0n1: 8 bytes were erased at offset 0x00000200 (gpt): 45 46 49 20 50 41 52 54
| /dev/nvme0n1: 8 bytes were erased at offset 0x3a38b2de00 (gpt): 45 46 49 20 50 41 52 54
| /dev/nvme0n1: 2 bytes were erased at offset 0x000001fe (PMBR): 55 aa
| /dev/nvme0n1: calling ioctl to re-read partition table: Success

FTR, when using wipefs' --force option, it still leaves behind the
LVM signatures anyways:

| root@grml ~ # pvs
|   PV             VG   Fmt  Attr PSize    PFree
|   /dev/nvme0n1p3 ngcp lvm2 a--  <232.41g <222.41g
| root@grml ~ # vgs
|   VG   #PV #LV #SN Attr   VSize    VFree
|   ngcp   1   1   0 wz--n- <232.41g <222.41g
| root@grml ~ # lvs
|   LV   VG   Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
|   root ngcp -wi-a----- 10.00g
| root@grml ~ # wipefs -a /dev/nvme0n1
| wipefs: error: /dev/nvme0n1: probing initialization failed: Device or resource busy
| 1 root@grml ~ # wipefs -af /dev/nvme0n1
| /dev/nvme0n1: 8 bytes were erased at offset 0x00000200 (gpt): 45 46 49 20 50 41 52 54
| /dev/nvme0n1: 8 bytes were erased at offset 0x3a38b2de00 (gpt): 45 46 49 20 50 41 52 54
| /dev/nvme0n1: 2 bytes were erased at offset 0x000001fe (PMBR): 55 aa
| root@grml ~ # pvs
|   PV             VG   Fmt  Attr PSize    PFree
|   /dev/nvme0n1p3 ngcp lvm2 a--  <232.41g <222.41g
| root@grml ~ # vgs
|   VG   #PV #LV #SN Attr   VSize    VFree
|   ngcp   1   1   0 wz--n- <232.41g <222.41g
| root@grml ~ # lvs
|   LV   VG   Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
|   root ngcp -wi-a----- 10.00g

So we'd still have to wipe the LVM signatures, while enabling wipefs' --force
option could lead to unexpected behaviors.

Verified with:

| root@grml ~ # wipefs --version
| wipefs from util-linux 2.36.1
| root@grml ~ # uname -a
| Linux web01a 5.10.0-6-amd64 #1 SMP Debian 5.10.28-1 (2021-04-09) x86_64 GNU/Linux
| root@grml ~ # lvm version | head -3
|   LVM version:     2.03.11(2) (2021-01-08)
|   Library version: 1.02.175 (2021-01-08)
|   Driver version:  4.43.0

Change-Id: Ie4f7b2797d2dcfc27601792d6102a765e4c60c47
(cherry picked from commit cf01ec9257)

templates/scripts/includes/deployment.sh

@@ -432,9 +432,6 @@ clear_partition_table() {
     die "Error: ${blockdevice} doesn't look like a valid block device." >&2
   fi
 
-  echo "Wiping disk signatures from ${blockdevice}"
-  wipefs -a "${blockdevice}"
-
   # make sure parted doesn't fail if LVM is already present
   blockdev --rereadpt "$blockdevice"
   for disk in "$blockdevice"* ; do
@@ -450,6 +447,9 @@ clear_partition_table() {
     pvremove "$disk" --force --force --yes || true
   done
 
+  echo "Wiping disk signatures from ${blockdevice}"
+  wipefs -a "${blockdevice}"
+
   dd if=/dev/zero of="${blockdevice}" bs=1M count=1
   blockdev --rereadpt "${blockdevice}"
 }