Add a regression test for PR 225547

zfsd(8) shouldn't add a spare to a replacing vdev

tests/sys/cddl/zfs/tests/zfsd/Makefile
tests/sys/cddl/zfs/tests/zfsd/zfsd_hotspare_008_neg.ksh
tests/sys/cddl/zfs/tests/zfsd/zfsd_test.sh
Add a test case to check that zfsd shouldn't activate a spare for a
child of a replacing vdev. Fixing zfsd itself is still TODO.

PR: 225547
Sponsored by: Spectra Logic Corp