ZTS: Adapt casenorm tests for FreeBSD

Several casenorm tests pass on FreeBSD but are expected to fail on
Linux.

Move the passing tests from "fail" to "maybe" so that passing on
FreeBSD is not unexpected.

Invert platform logic so FreeBSD doesn't use illumos-only zlook.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #10050