ZTS: Add known exceptions

Add the following test failures to the exception list for FreeBSD
to ensure we notice new unexpected failures.

   pool_checkpoint/checkpoint_big_rewind
   pool_checkpoint/checkpoint_indirect

And the following for Linux.

   zvol/zvol_misc/zvol_misc_snapdev

Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #12621
Issue #12622
Issue #12623
Closes #12624