Merge pull request #2290 from tedyu/get-container

vc: Use map built-in accessor to find container in Sandbox#GetContainer

virtcontainers/sandbox.go

@@ -279,11 +279,9 @@ func (s *Sandbox) GetAllContainers() []VCContainer {
 
 // GetContainer returns the container named by the containerID.
 func (s *Sandbox) GetContainer(containerID string) VCContainer {
-	for id, c := range s.containers {
-		if id == containerID {
+	if c, ok := s.containers[containerID]; ok {
 		return c
 	}
-	}
 	return nil
 }