If we dump tasks with mntns, we should look at pathes from point of a mntns root.

Now we support a situation when a root of an init task has the same root as the
mntns root, because we have not another way to get a root of mntns.

A path to an unix socket is copied, because the origin copy will be gone
out from the function, where it was created.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>