These were previously written in very convoluted C which had to deal
with parsing the crazy output of the "lvm" command. In fact the
parsing was so complex that it was generated by the generator. It's
easier to do this in OCaml.
These are basically legacy APIs. They cannot be expanded and LVM
already supports many more fields. We should replace these with APIs
for getting single named fields from LVM.
(cherry picked from commit a73f248369)
(cherry picked from commit 80b2fcb243)
c34a91bb23