Make sure filesystem is ready when volume becomes available.
Use 'write-once' as initial state for read-only volumes, only allow
writing to volumes in that state and transision to 'read-only' once
write has completed.
Also fix a typo which prevented 'list' command from working with LVM.

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

* use lvm --reportformat json
 * add 'list' and 'align' commands
 * add help output

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

uvol is a wrapper-script which allows automated handling of storage
volumes. uvol currently comes with backend support for LVM2 and UBI,
covering practically all options for storage large enough to be
managed (NAND, SPI-NAND, eMMC, SATA, NVME, virtio-blk, ...).

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