generic: test data integrity with mixed buffer read and aio dio write

generic: test data integrity with mixed buffer read and aio dio write

When mixing buffered reads and asynchronous direct writes, it is
possible to end up with the situation where we have stale data in
the page cache while the new data is already written to disk.

This issue should be fixed by patch titled:

fs: Fix page cache inconsistency when mixing buffered and AIO DIO

Signed-off-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>