exec: add ability to set file descriptors for stdin, stdout, stderr (v2)

v2: add separate functions, which take file descriptor array
Signed-off-by: Andrey Vagin <avagin@openvz.org>
exec: create a new session to execute anything in CT

I think it should be default behaviour due to security reason

Signed-off-by: Andrey Vagin <avagin@openvz.org>
libct: typo fix s/responce/response/

Signed-off-by: Andrey Vagin <avagin@openvz.org>
libct: local_enter_execve should call local_enter_cb

Signed-off-by: Andrey Vagin <avagin@openvz.org>
libct: set SOCK_CLOEXEC on sockets

We want to be sure, that children will not inherit these sockets.

Probably we need to think which file descriptors should be closed
in spawn_cb and enter_cb.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
go: reports errors from requests

Signed-off-by: Andrey Vagin <avagin@openvz.org>
go: handle interrupted connections

Signed-off-by: Andrey Vagin <avagin@openvz.org>
make: add -Wno-unused-result

It's enabled on Ubuntu by default.

Signed-off-by: Andrey Vagin <avagin@openvz.org>