Replace execdrivers with containerd implementation

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>
Signed-off-by: Anusha Ragunathan <anusha@docker.com>

libcontainerd/queue_linux.go

@@ -0,0 +1,29 @@
+package libcontainerd
+
+import "sync"
+
+type queue struct {
+	sync.Mutex
+	fns map[string]chan struct{}
+}
+
+func (q *queue) append(id string, f func()) {
+	q.Lock()
+	defer q.Unlock()
+
+	if q.fns == nil {
+		q.fns = make(map[string]chan struct{})
+	}
+
+	done := make(chan struct{})
+
+	fn, ok := q.fns[id]
+	q.fns[id] = done
+	go func() {
+		if ok {
+			<-fn
+		}
+		f()
+		close(done)
+	}()
+}