block-meta custom failed on kvm

[Jack Chen]

I used MAAS 2.4 and maas server is Ubuntu 18.04. I'm deploying ubuntu 16.04 on vm created on kvm. There are 4 disks on vm, vda (boot disk)...vdd. At some time the disk partition fix messed up by application deployer, the vm failed to deploy.

Curtin debug log sections:
```
        Running command ['lsblk', '--noheadings', '--bytes', '--pairs', '--output=ALIGNMENT,DISC-ALN,DISC-GRAN,DISC-MAX,DISC-ZERO,FSTYPE,GROUP,KNAME,LABEL,LOG-SEC,MAJ:MIN,MIN-IO,MODE,MODEL,MOUNTPOINT,NAME,OPT-IO,OWNER,PHY-SEC,RM,RO,ROTA,RQ-SIZE,SIZE,STATE,TYPE,UUID'] with allowed return codes [0] (capture=True)

        Checking if /dev/vdc2 is a swap device

        finish: cmd-install/stage-partitioning/builtin/cmd-block-meta: FAIL: removing previous storage devices

        finish: cmd-install/stage-partitioning/builtin/cmd-block-meta: FAIL: curtin command block-meta

        Traceback (most recent call last):

          File "/curtin/curtin/commands/main.py", line 201, in main

            ret = args.func(args)

          File "/curtin/curtin/commands/block_meta.py", line 58, in block_meta

            meta_custom(args)

          File "/curtin/curtin/commands/block_meta.py", line 1471, in meta_custom

            clear_holders.clear_holders(disk_paths)

          File "/curtin/curtin/block/clear_holders.py", line 587, in clear_holders

            shutdown_function(dev_info['device'])

          File "/curtin/curtin/block/clear_holders.py", line 310, in wipe_superblock

            if is_swap_device(blockdev):

          File "/curtin/curtin/swap.py", line 108, in is_swap_device

            decode=False)

          File "/curtin/curtin/util.py", line 549, in load_file

            fp.seek(offset)

        OSError: [Errno 22] Invalid argument

        [Errno 22] Invalid argument

Stderr: ''

```

I got partition informations after using rescuing mode in MAAS:
```
$ sudo fdisk -l
Disk /dev/loop0: 158 MiB, 165711872 bytes, 323656 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/vda: 20 GiB, 21474836480 bytes, 41943040 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x4c8357c6

Device Boot Start End Sectors Size Id Type
/dev/vda1 2048 41943006 41940959 20G 83 Linux

Disk /dev/vdb: 100 GiB, 107374182400 bytes, 209715200 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 8F0B48D2-6AF7-472A-AB23-149308740E48

Device Start End Sectors Size Type
/dev/vdb1 2048 206847 204800 100M Ceph OSD
/dev/vdb2 206848 209715166 209508319 99.9G unknown

Disk /dev/vdc: 100 GiB, 107374182400 bytes, 209715200 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: BE4B2B10-EA65-4065-BFE6-8340F77B0374

Device Start End Sectors Size Type
/dev/vdc1 2048 20973567 20971520 10G unknown
/dev/vdc2 20973568 20973568 1 512B unknown
/dev/vdc3 20975616 41947135 20971520 10G unknown
/dev/vdc4 41947136 44044287 2097152 1G unknown
/dev/vdc5 44044288 44249087 204800 100M Ceph OSD
/dev/vdc6 44249088 209715166 165466079 78.9G unknown

Disk /dev/vdd: 100 GiB, 107374182400 bytes, 209715200 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: AFEA47AA-B4C4-44D3-8674-D84A53B104AB

Device Start End Sectors Size Type
/dev/vdd1 2048 20973567 20971520 10G unknown

```

After I manually deleted 6 partions on /dev/vdc, redeploy will success.

[Jack Chen (scsvip)]

This is duplicate with 1803672, so please close it