I recently made some bug fixes in nvmecontrol. It occurred to
me that since nvmecontrol lacks any kyua tests, I should convert the
informal testing I did into a more formal automated test. The test in
this change should be considered just a starting point; it is neither
complete nor thorough. While converting the test to ATF/kyua, I
discovered a small bug in nvmecontrol; the nvmecontrol devlist
command would always exit with an unsuccessful status. So I included
the fix for that, too, so that the test won't fail.

Run the test.