nsinit: Add Makefile

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Andrew Vagin <avagin@openvz.org>
nsinit: use the new API for executing processes

Signed-off-by: Andrey Vagin <avagin@openvz.org>
linux_container: ct.Destroy() returns error if CT isn't stopped
linux_factory: add StartInitialization()

After forking a new processes in a new container, we need to call exec()
and tune namespaces.
linux_container: execute an init process in a new CT

Here is a first step to implement a new API. Currently the init
processes is executed without namespaces and cgroups.

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