mkswap: zap bootbits

mkswap: zap bootbits

/dev/sdb1 originally initialized by cryptsetup:

and OLD mkswap:

        # vol_id /dev/sdb1 | grep TYPE
        ID_FS_TYPE=swap

        # blkid -s TYPE /dev/sdb1
        /dev/sdb1: TYPE="crypt_LUKS"

So, we have two different *valid* signatures on the device now!

NEW mkswap:

        # blkid -s TYPE /dev/sdb1
        /dev/sdb1: TYPE="swap"

        # /lib/udev/vol_id /dev/sdb1 | grep TYPE
        ID_FS_TYPE=swap

the bootbits (first 1024 bytes) was erased.

We shouldn't zap disk labels (BSD, SUN, ...) and boot loaders (on whole
disk):

        # mkswap  /dev/sdb2
        mkswap: /dev/sdb2: warning: don't erase bootbits sectors
                (BSD partition table detected). Use -f to force.
        Setting up swapspace version 1, size = 4348 KiB
        no label, UUID=69d87cef-71ac-4fb0-a689-ce3e930dea17

        # mkswap  /dev/sdb
        mkswap: /dev/sdb: warning: don't erase bootbits sectors
                on whole disk. Use -f to force.
        Setting up swapspace version 1, size = 8188 KiB
        no label, UUID=97757ad7-8a84-43d9-bcb4-16fefd93a2ac

Signed-off-by: Karel Zak <kzak@redhat.com>