pass address of metaHeaders to GetenvJson in ImagePush and ImagePull

Docker-DCO-1.1-Signed-off-by: kies <lleelm@gmail.com> (github: kieslee)

server/server.go

@@ -1381,7 +1381,7 @@ func (srv *Server) ImagePull(job *engine.Job) engine.Status {
 	}
 
 	job.GetenvJson("authConfig", authConfig)
-	job.GetenvJson("metaHeaders", metaHeaders)
+	job.GetenvJson("metaHeaders", &metaHeaders)
 
 	c, err := srv.poolAdd("pull", localName+":"+tag)
 	if err != nil {
@@ -1611,7 +1611,7 @@ func (srv *Server) ImagePush(job *engine.Job) engine.Status {
 
 	tag := job.Getenv("tag")
 	job.GetenvJson("authConfig", authConfig)
-	job.GetenvJson("metaHeaders", metaHeaders)
+	job.GetenvJson("metaHeaders", &metaHeaders)
 	if _, err := srv.poolAdd("push", localName); err != nil {
 		return job.Error(err)
 	}