Add support for zfs-localPV

[vharsh]

The pool listing for zfs-pool can be clubbed into the kubectl openebs get pool --cas-type=zfspool(but it'd lack the status field, which CStor field already has). As of now, we are not sure if zfs pool listing should go in the same sub-command(simpler UX of the CLI) or a new one(kubectl openebs get zfspool).

Features

• Volume listing
• Pool listing
• Volume describe
• Pool describe