format: Set MBR partition type byte appropriately (RHBZ#1000428).

Windows won't see a filesystem unless the MBR partition type
byte is set correctly.

$ ./run ./format/virt-format -a /tmp/test.img
$ ./run ./cat/virt-filesystems -a /tmp/test.img --all --long -h
Name       Type        VFS      Label  MBR  Size  Parent
/dev/sda1  filesystem  unknown  -      -    1.0G  -
/dev/sda1  partition   -        -      83   1.0G  /dev/sda
/dev/sda   device      -        -      -    1.0G  -

$ ./run ./format/virt-format -a /tmp/test.img --filesystem=ntfs
$ ./run ./cat/virt-filesystems -a /tmp/test.img --all --long -h
Name       Type        VFS   Label  MBR  Size  Parent
/dev/sda1  filesystem  ntfs  -      -    1.0G  -
/dev/sda1  partition   -     -      07   1.0G  /dev/sda
/dev/sda   device      -     -      -    1.0G  -

$ ./run ./format/virt-format -a /tmp/test.img --filesystem=vfat
$ ./run ./cat/virt-filesystems -a /tmp/test.img --all --long -h
Name       Type        VFS   Label  MBR  Size  Parent
/dev/sda1  filesystem  vfat  -      -    1.0G  -
/dev/sda1  partition   -     -      0b   1.0G  /dev/sda
/dev/sda   device      -     -      -    1.0G  -

$ ./run ./format/virt-format -a /tmp/test.img --lvm --filesystem=vfat
$ ./run ./cat/virt-filesystems -a /tmp/test.img --all --long -h
Name        Type        VFS   Label  MBR  Size   Parent
/dev/VG/LV  filesystem  vfat  -      -    1020M  -
/dev/VG/LV  lv          -     -      -    1020M  /dev/VG
/dev/VG     vg          -     -      -    1020M  /dev/sda1
/dev/sda1   pv          -     -      -    1020M  -
/dev/sda1   partition   -     -      8e   1.0G   /dev/sda
/dev/sda    device      -     -      -    1.0G   -

Thanks: Gerd Hoffmann (kraxel)
format: Add --label option for setting filesystem label.

$ ./run ./format/virt-format -a /tmp/test.img --filesystem=ext2 --label=BOOT
$ ./run ./cat/virt-filesystems -a /tmp/test.img --all --long -h
Name       Type        VFS   Label  MBR  Size  Parent
/dev/sda1  filesystem  ext2  BOOT   -    1.0G  -
/dev/sda1  partition   -     -      83   1.0G  /dev/sda
/dev/sda   device      -     -      -    1.0G  -

Thanks: Gerd Hoffmann (kraxel)
virt-make-fs: Add --label option for setting filesystem label.

$ ./run ./tools/virt-make-fs /tmp/supermin-4.1.4.tar.gz /tmp/test.img
$ ./run ./cat/virt-filesystems -a /tmp/test.img --all --long -h
Name      Type        VFS   Label  MBR  Size  Parent
/dev/sda  filesystem  ext2  -      -    3.7M  -
/dev/sda  device      -     -      -    3.7M  -

$ ./run ./tools/virt-make-fs /tmp/supermin-4.1.4.tar.gz /tmp/test.img --label=BOOT
$ ./run ./cat/virt-filesystems -a /tmp/test.img --all --long -h
Name      Type        VFS   Label  MBR  Size  Parent
/dev/sda  filesystem  ext2  BOOT   -    3.7M  -
/dev/sda  device      -     -      -    3.7M  -

Thanks: Gerd Hoffmann (kraxel)
daemon: Allow labels to be set on DOS filesystems using 'dosfslabel'.

You can now use virt-format or virt-make-fs --label option to set a
label for a DOS filesystem:

$ ./run ./format/virt-format -a /tmp/test.img --filesystem=vfat --label=BOOT
$ ./run ./cat/virt-filesystems -a /tmp/test.img --all --long -h
Name       Type        VFS   Label  MBR  Size  Parent
/dev/sda1  filesystem  vfat  BOOT   -    1.0G  -
/dev/sda1  partition   -     -      0b   1.0G  /dev/sda
/dev/sda   device      -     -      -    1.0G  -

This also contains a small code refactoring.

Thanks: Gerd Hoffmann (kraxel)