Use sfdisk to get GPT partition by name as partition names are not
known by the kernel if added via partx.
Make sure physical volume names are unique, if possible correlate
with the disks serial number and/or card's cid.
mkf2fs apparently returns 134 even in case format succeeded, so don't
fail in that case (this fixes rw volumes large enough for F2FS to be
selected by the lvm scripts of uvol).

Signed-off-by: Daniel Golle <daniel@makrotopia.org>