Extend and rename zfsobj2fid

Teach the script to get FIDs using the getfattr command given a Lustre
object number.  This is considerably faster than zdb and saves the user
from having to first get the ZFS inode number of the Lustre object.
Rename the script from zfsobj2fid to obj2fid since it now understands
Lustre or ZFS numbers.

In addition, always set the "version" field of the printed FID to zero.
Some OST objects have a non-zero version field, though I don't know why
because the Lustre code comments say that field is currently unused. In
any case, "lfs fid2path" doesn't understand this and rejects any FID
with a non-zero version, so we'll just ignore whatever might be stored
there.