Async dirops have been supported in mainline kernels for quite some time
now, and we've recently (as of June) started doing regular testing in
teuthology with '-o nowsync'. There were a few issues, but we've sorted
those out now.

Enable async dirops by default, and change /proc/mounts to show "wsync"
when they are disabled rather than "nowsync" when they are enabled.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>