Revisiting the ZFS test suite

[Alan Somers]

My employment status changed last week, and I find myself once again
working on ZFS.  It's hard to have confidence in any changes without a
solid test suite, so my main task right now is to fix the problems in
FreeBSD's ZFS test suite.  Our most recent run had 64 failed tests and 99
skipped ones; let's get those down to 0 and something small, respectively.

https://ci.freebsd.org/job/FreeBSD-head-amd64-test_zfs/3880/testReport/

Would anybody be interested to review my changes to the test suite?  It's
not terrible if I have to commit without review; I can't possibly break
anything but the test suite itself.

-Alan