zed: update zed.d/statechange-slot_off.sh

The statechange-slot_off.sh zedlet which was added in #15200
needed to be installed so it's included by the packages.

Additional testing has also shown that multiple retries are
often needed for the script to operate reliably.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #15210