vzctl: synchronize CRIU with vzctl (v2)

vzctl provides two descriptors signalfd and waitfd, it's used for apply
host-side configuration after creating environment.
A signal is send to signalfd after creating environment and an answer is
recieved from waitfd.

v2: fix comments from Kir

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
4 files changed