[PATCH] Change O_DIRECT vs buffered setup

[PATCH] Change O_DIRECT vs buffered setup

Change the default from O_DIRECT IO to normal buffered IO. That makes
more sense, as O_DIRECT is a special case and should be manually
enabled as such.

Do this by adding a option negate switch, so we don't need two sets
of parameters to control these options.

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