Merge SPA version 25 support from IllumOS

6675946 'zpool status' should show the progress of resilvering for individual disk.
6683750 scrub -s have to wait until resilver completed?
6841252 Resilvering not restartable - causing an excess reboot delay
6855073 spa scrub stats (eg %done) are reset on reboot
6891824 7410 NAS head "continually resilvering" following HDD replacement
6899970 scrub/resilver percent complete reporting in zpool status can be overly optimistic
6940889 add interval (count) args to zpool list
6944623 dbuf_read_done() locking performance improvement
6946760 mutex problem in bplist_enqueue()
6391915 RFE: provide interval arg to zpool status to monitor resilvering
6946512 want zfs_send() to pass back debug info
6943992 'zpool scrub' should not restart the existing scrub silently
6878281 zpool should store the time of last scrub/resilver and other zpool status info in pool properties.
6935158 Assertion failed: used <= spa_get_dspace(dd->dd_pool->dp_spa)
6944388 dsl_dataset_snapshot_reserve_space() causes dp_write_limit=max