11682 zpool iostat and status improvements
Review Request #2478 - Created Jan. 6, 2020 and updated
Port from OpenZFS of a set of zpool 'iostat' and 'status' enhancements. Also added kstats in the places where the code was originally using Linux /proc to expose various state. Also updated various zfs-test cases to remove old workaround for the previously missing zpool iostat handling (this brings these test back into closer alignment with OpenZFS).
Rebased and fixed some smatch issues.
Revision 2 (+3411 -615)