Add scrub after resilver zed script

Add scrub after resilver zed script

* Add a zed script to kick off a scrub after a resilver.  The script is
disabled by default.

* Add a optional $PATH (-P) option to zed to allow it to use a custom
$PATH for its zedlets.  This is needed when you're running zed under
the ZTS in a local workspace.

* Update test scripts to not copy in all-debug.sh and all-syslog.sh by
default.  They can be optionally copied in as part of zed_setup().
These scripts slow down zed considerably under heavy events loads and
can cause events to be dropped or their delivery delayed. This was
causing some sporadic failures in the 'fault' tests.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #4662
Closes #7086