ZTS: Tests using zhack may fail on FreeBSD

As described in #11854, zhack is occasionally segfaulting on FreeBSD.
Debugging this is proving to be tricky. To avoid false positives in
the CI add entries for the tests that use zhack in zts-report to
accept that they may occasionally fail on FreeBSD.

Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Issue #11854
Closes #11855