add pre-dump and parent-path to checkpoint

CRIU gets pre-dump to complete iterative migration.
pre-dump saves process memory info only. And it need parent-path
to specify the former memory files.

This patch add pre-dump and parent-path arguments to runc checkpoint

Signed-off-by: Deng Guangxing <dengguangxing@huawei.com>
Signed-off-by: Adrian Reber <areber@redhat.com>

man/runc-checkpoint.8.md

@@ -13,11 +13,13 @@ checkpointed.
 # OPTIONS
    --image-path value           path for saving criu image files
    --work-path value            path for saving work files and logs
+   --parent-path value          path for previous criu image files in pre-dump
    --leave-running              leave the process running after checkpointing
    --tcp-established            allow open tcp connections
    --ext-unix-sk                allow external unix sockets
    --shell-job                  allow shell jobs
    --page-server value          ADDRESS:PORT of the page server
    --file-locks                 handle file locks, for safety
+   --pre-dump                   dump container's memory information only, leave the container running after this
    --manage-cgroups-mode value  cgroups mode: 'soft' (default), 'full' and 'strict'
    --empty-ns value             create a namespace, but don't restore its properies