Add .gitignore files
Add code comment for _get_iops()
Ignore missing brw_stats in the osd directories.

As of 2.3.64 (probably earlier too) we have lost obdfilter's brw_stats,
and the new OSD proc directories lack that file, or any other clear
way to get the information that we need.
Bump version to 3.1.6 and run autogen.sh