Currently criu can't handle a processes with more than 1024
file descriptors.

In this patch, criu dumps file descriptors for a few iterations.

Fixes https://github.com/xemul/criu/issues/145

v2: don't move the collect stage
Signed-off-by: Andrew Vagin <avagin@virtuozzo.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>