Step: mkfs
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Create a filesystem.

Step keys:

* `mkfs` &mdash; REQUIRED; filesystem type, such as `ext4` or `vfat`.

* `partition` &mdash; REQUIRED; tag for the block device to use.

* `options` &mdash; OPTIONAL; aditional options for mkfs.

* `target_old` &mdash; OPTIONAL; avoids using `ext4` options that are
  incompatible with older (Debian Buster or earlier) systems.

Example (in the .vmdb file):

    - mkfs: ext4
      partition: root
      options: -O ^64bit,^metadata_csum
