libblkid: try to detect if PT is newer than LVM

libblkid: try to detect if PT is newer than LVM

LVM (pvcreate) wipes the begin of the device. If there is a PT in the
wiped area then LVM signature is obsolete.

 # pvcreate /dev/sdb
 # fdisk /dev/sdb

old version:
 # blkid -p -o udev /dev/sdb
 ID_FS_TYPE=LVM2_member

new version:
 # blkid -p -o udev /dev/sdb
 ID_PART_TABLE_TYPE=dos

Reported-by: Matej Cepl <mcepl@redhat.com>
Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=679799
Signed-off-by: Karel Zak <kzak@redhat.com>