ZTS: import_rewind_device_replaced reliably fails

The import_rewind_device_replaced.ksh test was never entirely reliable
because it depends on MOS data not being overwritten. The MOS data is
not protected by the snapshot so occasional failures were always
expected. However, this test is now failing reliably on all platforms
indicating something has changed in the code since the test was marked
"maybe". Convert the test to a "known" failure until the root cause
is identified and resolved.

Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #12821