MFC r329690: MFV r319737: 6939 add sysevents to zfs core for commands

MFC r329690: MFV r319737: 6939 add sysevents to zfs core for commands

illumos/illumos-gate@ce1577b04976f1d8bb5f235b6eaaab15b46a3068
https://github.com/illumos/illumos-gate/commit/ce1577b04976f1d8bb5f235b6eaaab15b46a3068

https://www.illumos.org/issues/6939
  Originally created https://smartos.org/bugview/OS-4489
       sysevents should be fired in the kernel from ZFS whenever a command
       is run that is logged in zpool history.
  Example output
  Terminal 1
  root - gz sunos ~ # zfs create zones/foobar
  root - gz sunos ~ # zfs set quota=10g zones/foobar
  root - gz sunos ~ # zfs destroy zones/foobar
  Terminal 2
  root - gz sunos ~ # sysevent EC_zfs
  nvlist version: 0
      date = 2016-04-28T14:50:08.964Z
      vendor = SUNW
      publisher = zfs
      class = EC_zfs
      subclass = ESC_ZFS_history_event
      pid = 0
      data = (embedded nvlist)
      nvlist version: 0
          pool_name = zones
          pool_guid = 0x40c964e8f9a7a694
          history_record = (embedded nvlist)
          nvlist version: 0
              dsname = zones/foobar
              dsid = 0x1525
              history internal str =
              internal_name = create
              history txg = 0x4c4ef3

Reviewed by: Patrick Mooney <patrick.mooney@joyent.com>
Reviewed by: Joshua M. Clulow <jmc@joyent.com>
Reviewed by: Josh Wilsdon <jwilsdon@joyent.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed by: Alan Somers <asomers@gmail.com>
Reviewed by: Andrew Stormont <andyjstormont@gmail.com>
Approved by: Matthew Ahrens <mahrens@delphix.com>
Author: Dave Eddy <dave@daveeddy.com>