* Don't partition a disk if too few are available. Just rely on Kyua to
ensure that the tests aren't run with insufficient disks.
* Remove redundant cleanup steps
* In zpool_add_003_pos, store the temporary file in $PWD so Kyua will
automatically clean it up.
* Update zpool_add_005_pos to use dumpon instead of dumpadm. This test had
never been ported to FreeBSD.
* In zpool_add_005_pos, don't format the dump disk with UFS. That was
pointless.
MFC after: 2 weeks
Sponsored by: Axcient
e2032bdaaa