Clustered LVM storage driver

[stgraber]

Implement a new derivative of the lvm storage driver which makes use of lvmlockd and sanlock to provide a remote storage driver that's based on a shared block device.

Such a block device can come from a Fiber Channel LUN, iSCSI share, NVMEoF/NVMEoTCP drive or any other mechanism to provide a writable consistent block device across multiple servers.

This storage driver should be quite small and simple as it will build on top of the existing local LVM driver.