zfs: Make zpool and zfs list work

$ ./scripts/run.py -e 'zpool.so list'
OSv v0.08-81-gc3422a7
eth0: 192.168.122.15
NAME   SIZE  ALLOC   FREE    CAP  DEDUP  HEALTH  ALTROOT
osv   9.94G   148M  9.79G     1%  1.00x  ONLINE  -

$ ./scripts/run.py -e 'zfs.so list'
OSv v0.08-81-gc3422a7
eth0: 192.168.122.15
NAME      USED  AVAIL  REFER  MOUNTPOINT
osv       148M  9.64G    32K  /
osv/zfs   148M  9.64G   148M  /zfs

Enable it by compiling the missing functions.

Reviewed-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Asias He <asias@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>