zed: Take no action on scrub/resilver checksum errors

zed: Take no action on scrub/resilver checksum errors

When scrubbing/resilvering a pool it can be counter productive to
cancel the scan and kick of a replace operation to a hot spare
when encountering checksum errors.  In this case, the best course
of action is to allow the scrub/resilver to complete as quickly
as possible and to keep the vdevs fully online if possible.

Realistically, this is less of an issue for a RAIDZ since a
traditional resilver must be used and checksums will be verified.
However, this is not the case for a mirror or dRAID pool which is
sequentially resilvered and checksum verification is deferred
until after the replace operation completes.

Regardless, we apply this policy to all pool types since it's
a good idea for all vdevs.  Degrading additional vdevs has the
potential to make a bad situation worse.  Note the checksum
errors will still be reported as both an event and by
`zpool status`.  This change only prevents the ZED from
proactively taking any action.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #13499