dump: Unlock network if -R option passed

It's been found that if -R (leave task running after checkpoint)
option passed we don't unlock network, nether we clean service
files (such as link remaps).

After a long discussion we choose the following path: if -R option
is passed, it means a user is quite confident in what he is doing
and consistency of the resources (file system) is achieved by
a user himself with help of post-dump script. Also a user knows
that the network will be unlocked and accept such case.

So here we check of -R being passed in command line and once
checkpoint complete we unlock the network.

Cleaning up of link remaps is addressed in another patch.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>