tools/hotplug/Linux: allow hardlinked files for block device images

tools/hotplug/Linux: allow hardlinked files for block device images

tools/hotplug/Linux/block change for this losetup -a output:
(inode 12 is listed twice due to hardlinks)

/dev/loop0: [0809]:139267 (/abuild/vdisk-sles11_2-disk0)
/dev/loop1: [0809]:139266 (/abuild/vdisk-sles11_1-disk1)
/dev/loop3: [0809]:139267 (/abuild/vdisk-sles11_2-disk0)
/dev/loop5: [0809]:139273 (/abuild/vdisk-sles11_5-disk1)
/dev/loop8: [0809]:12 (/abuild/bootiso-xenpaging-sles11_5.iso)
/dev/loop10: [0809]:12 (/abuild/bootiso-xenpaging-sles11_4.iso)
/dev/loop11: [0809]:139271 (/abuild/vdisk-sles11_4-disk0)

Without this change, $dev would contain /dev/loop8\n/dev/loop10
Applies to 4.0 and 4.1

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>