virt-filesystems: Add MBR partition type byte to the output.

virt-filesystems: Add MBR partition type byte to the output.

This adds an extra column containing this information, looking
like this:

Name       Type        VFS   Label  MBR  Size  Parent
/dev/sda1  filesystem  ntfs  -      -    6.0G  -
/dev/sda1  partition   -     -      07   6.0G  /dev/sda
/dev/sda   device      -     -      -    6.0G  -

In particular you can use this to tell if a partition is an extended
partition, because the field will contain '05' or '0f'.