Cleanup the parallellized log writing

And move it all to iolog.c, this means we can un-export
some of the log functions, too.

Signed-off-by: Jens Axboe <axboe@fb.com>
crc: add test.h header to test.c

This way the static analyzers know that there's a reason
for the exported function.

Signed-off-by: Jens Axboe <axboe@fb.com>
iolog: invert log_mask bits

Get rid of the all-log-mask.

Signed-off-by: Jens Axboe <axboe@fb.com>