Merge vendor bugfix for ZFS test suite that triggers false positives.
Illumos ZFS issues:
3949 ztest fault injection should avoid resilvering devices
3950 ztest: deadman fires when we're doing a scan
3951 ztest hang when running dedup test
3952 ztest: ztest_reguid test and ztest_fault_inject don't place nice together
4f7b34578b