linux_factory: add StartInitialization()

After forking a new processes in a new container, we need to call exec()
and tune namespaces.

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

factory.go

@@ -27,4 +27,14 @@ type Factory interface {
 	// Container is stopped
 	// System error
 	Load(id string) (Container, error)
+
+        // StartInitialization is an internal API to libcontainer used during the rexec of the
+        // container.  pipefd is the fd to the child end of the pipe used to syncronize the  
+        // parent and child process providing state and configuration to the child process and
+        // returning any errors during the init of the container
+        //
+        // Errors:
+        // pipe connection error
+        // system error
+        StartInitialization(pipefd uintptr) error
 }