- docs/formatstorage.html.in: document 'zfs' pool type, add it
to a list of pool types that could use source physical devices
- docs/storage.html.in: update a ZFS pool example XML with
source physical devices, mention that starting from 1.2.9 a
pool could be created from this devices by libvirt and in earlier
versions user still has to create a pool manually
- docs/drvbhyve.html.in: add an example with ZFS pools
