Merge branch 'sgunmap2' of https://github.com/vincentkfu/fio

Merge branch 'sgunmap2' of https://github.com/vincentkfu/fio

* 'sgunmap2' of https://github.com/vincentkfu/fio:
  docs: update HOWTO and manpage for sg trim support
  testing: add test scripts for sg ioengine
  engines/sg: move asserts and debug statements behind a debug flag
  engines/sg: add cmdp and dxferp for trims to sg error string
  engines/sg: support trim operations via the UNMAP command
  stat: add IO submit and complete depths to JSON output
  ioengines: have ioengines with commit do own io accounting for trims