Move supervisor to it's own package

It allows to keep main namespace cleaner

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

supervisor/add_process.go

@@ -0,0 +1,36 @@
+package supervisor
+
+import "github.com/Sirupsen/logrus"
+
+type AddProcessEvent struct {
+	s *Supervisor
+}
+
+// TODO: add this to worker for concurrent starts???  maybe not because of races where the container
+// could be stopped and removed...
+func (h *AddProcessEvent) Handle(e *Event) error {
+	ci, ok := h.s.containers[e.ID]
+	if !ok {
+		return ErrContainerNotFound
+	}
+	p, io, err := h.s.runtime.StartProcess(ci.container, *e.Process, e.Console)
+	if err != nil {
+		return err
+	}
+	if e.Pid, err = p.Pid(); err != nil {
+		return err
+	}
+	h.s.processes[e.Pid] = &containerInfo{
+		container: ci.container,
+	}
+	l, err := h.s.copyIO(e.Stdin, e.Stdout, e.Stderr, io)
+	if err != nil {
+		// log the error but continue with the other commands
+		logrus.WithFields(logrus.Fields{
+			"error": err,
+			"id":    e.ID,
+		}).Error("log stdio")
+	}
+	h.s.processes[e.Pid].copier = l
+	return nil
+}