remove reflection and just use switches. 

 a little brute force, but more understandable.

Loops in zpool list, but eliminates a lot of other cruft.
I see it was also ignored before, but ignoring the error return here makes me a bit uneasy.  Though chances are pretty damned good that `zfs` won't ever do anything unpredictable like return `quota=HELLOWORLD`, it may still be worth checking for those extreme cases.

To avoid having to bubble the error all the way up for such a bizarre scenario, this may even be a good use for `panic()`.  Chances are pretty good that if your ZFS installation is hosed to the point where it thinks a quota is a string, it'll gladly do some damage to your zpool(s), and should fail as fast and loud as possible.