dasd: fix ped_disk_new_fresh to not read old data from disk

dasd: fix ped_disk_new_fresh to not read old data from disk

dasd_write(), was reading the volume label from the disk (trough
fdasd_check_volume()) and later writing it back again, this is fine for
existing dasd labels, but when creating a fresh label, this would
also cause the old volume label to be re-used, and if the old label
was corrupt, it would cause fdasd_check_volume() and thus dasd_write()
to fail.  Reported here: http://bugzilla.redhat.com/533808

* libparted/arch/linux.c: include fdasd.h.
(init_dasd): Do BIODASDINFO ioctl, and store the dasd devno in
arch_specific.
(init_dasd): Remove dead (never reached) code.
* libparted/arch/linux.h (struct _LinuxSpecific): Add devno member.
* libparted/labels/dasd.c (DasdDiskSpecific): add vlabel member.
(dasd_alloc): Init DasdDiskSpecific.vlabel for fresh disks
(dasd_read): Store read vlabel in DasdDiskSpecific.vlabel.
(dasd_write): Write DasdDiskSpecific.vlabel instead of on disk vlabel.