Merge pull request #672 from rajasec/userns-validation

handling error for userns

libcontainer/specconv/spec_linux.go

@@ -540,10 +540,6 @@ func setupUserNamespace(spec *specs.Spec, config *configs.Config) error {
 	if len(spec.Linux.UIDMappings) == 0 {
 		return nil
 	}
-	// do not override the specified user namespace path
-	if config.Namespaces.PathOf(configs.NEWUSER) == "" {
-		config.Namespaces.Add(configs.NEWUSER, "")
-	}
 	create := func(m specs.IDMapping) configs.IDMap {
 		return configs.IDMap{
 			HostID:      int(m.HostID),