vzctl start/destroy: fix criu dump removal

In case we do checkpointing via criu, our "dumpfile" is
actually a directory and we need to remove it recursively.

1 Fix destroy_dumpfile() accordingly
2 Rename to destroy_dump()
3 Use it from vps_start()

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
3 files changed