zfsd(8) should activate spares at startup

cddl/sbin/zfsd/zfsd.cc
On startup, or after the devd event buffer overflows, generate
synthetic config_sync events for every zpool. This will force any
open casefiles on those pools to be reevaluated. This fixes a bug
where zfsd wouldn't activate a spare for disks that failed while
zfsd was not running, or if the disk failure generated an event
storm that caused zfsd to drop devd events.

tests/sys/cddl/zfs/tests/zfsd/zfsd_test.sh
Clear the expected failure

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