xfstest: add fallocate/truncate vs AIO/DIO stress test

xfstest: add fallocate/truncate vs AIO/DIO stress test

Run DIO, fallocate and truncate threads on a common file in parallel.
If a race exists, the old dio request may rewrite blocks after it was
allocated to another file, we will catch that by verifying blocks content.

this patch known to catch deadlock for ext4
http://lists.openwall.net/linux-ext4/2012/09/06/3

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>