10952 defer new resilvers and misc. resilver-related fixes
illumos/illumos-gate@e4c795beb33bf59dd4ad2e3f88f493111484b890
https://github.com/illumos/illumos-gate/commit/e4c795beb33bf59dd4ad2e3f88f493111484b890
https://www.illumos.org/issues/10952
From ZoL 612c4930dd2 Fix the spelling of deferred ??? cef48f14da6 Remove races from scrub / resilver tests 4021ba4cfaa Make vdev_set_deferred_resilver() recursive 8cb119e3dc0 Fix 2 small bugs with cached dsl_scan_phys_t 5e0bd0ae056 Fix issue with scanning dedup blocks as scan ends b3d7725c943 Remove zfs_gitrev.h (this shouldn't be part of 80a91e74696) 80a91e74696 Defer new resilvers until the current one ends
Portions contributed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Portions contributed by: Brian Behlendorf <behlendorf1@llnl.gov>
Portions contributed by: Arkadiusz Bubała <arkadiusz.bubala@open-e.com>
Author: Tom Caputi <tcaputi@datto.com>