criu: mem: count all pages actually written to image as "pages_written"

Currently potentially lazy pages are not counted as written even if they
are dump into pages*img. Count these pages as "pages_written" when dump is
not going to skip writing lazy pages to disk.

travis-ci: success for criu: mem: count all pages actually written to image as "pages_written"
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>