usr.sbin/makefs: Add HAMMER2 offline destroy support
The offline destroy takes HAMMER2 specific "-o D" option.
`image-file` argument is a valid HAMMER2 image file or block device.
`directory` argument is unused, but needs to be a valid path or "--".
e.g.
$ makefs -t hammer2 -o D=/a.out /dev/adx --
$ makefs -t hammer2 -o D=1234 /path/to/hammer2.img --
The "-o D" option reuires file path or inode number argument.
- If it's a file path, optarg must start with '/'.
- If it's an inum, optarg must start with "0x" or '0'-'9'.
Note that destroy by inum seems broken not only in makefs, but also
in real HAMMER2 ioctl.