11770 additional mmp fixes
illumos/illumos-gate@4348eb901228d2f8fa50bb132a34248e8662074e
https://github.com/illumos/illumos-gate/commit/4348eb901228d2f8fa50bb132a34248e8662074e
https://www.illumos.org/issues/11770
Port a few additional MMP fixes from ZoL that came in after our initial MMP port. 4ca457b065 ZTS: Fix mmp_interval failure ca95f70dff zpool import progress kstat (only minimal changes from above can be pulled in right now) 060f0226e6 MMP interval and fail_intervals in uberblock
Portions contributed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Portions contributed by: Brian Behlendorf <behlendorf1@llnl.gov>
Author: Olaf Faaland <faaland1@llnl.gov>