generic: add test for truncate/collapse range race

generic: add test for truncate/collapse range race

This case tests truncate/collapse range race. If the race occurs, it
will trigger a BUG_ON(). And this kernel patch has fixed this race:
    23fffa9 fs: move falloc collapse range check into the filesystem methods

Signed-off-by: Xiaoguang Wang <wangxg.fnst@cn.fujitsu.com>
Signed-off-by: Xing Gu <gux.fnst@cn.fujitsu.com>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>