This fixes the test-charset-fidelity test case.  A simpler example
which fails without this is:

  guestfish <<EOF
  sparse test1.img 1G
  run
  part-disk /dev/sda mbr
  mkfs msdos /dev/sda1
  mount /dev/sda1 /
  touch /foo
  umount /
  mkfs ntfs /dev/sda1
  # Next command would fail:
  mount /dev/sda1 /
  vfs-type /dev/sda1 -x
  EOF

Old blkid in RHEL 5 didn't return the right thing for PVs.

The original fix for this in
commit 511c82df46f5c6f4a7f984fdb81d4691038ed6da was not complete, in
that it did not fix the case of the old (pre '-m' option) parted.
This doesn't matter for Fedora, but it matters for RHEL 5 which has
this ancient parted.

This returns the index of the device, eg. /dev/sdb => 1.
Or you can think of it as the order that the device was
added, or the index of the device in guestfs_list_devices.

Thanks Alasdair Kergon.

Sort the device names correctly, not just treating them as
strings.  As a result, /dev/sdz < /dev/sdaa.

Apparently e2fsprogs only knows that "/dev/sda" is a whole device, but
doesn't think that "/dev/vda" is.  On switching the default device
over to virtio-scsi, that causes mke2fs without -F option to complain
and ask for an interactive prompt.  Adding -F forces it to go ahead
anyway.

This caused several less-used APIs to break with virtio-scsi.