cmd/ctr, service/containers: implement container filter

Signed-off-by: Stephen J Day <stephen.day@docker.com>

cmd/ctr/utils.go

@@ -247,3 +247,28 @@ func replaceOrAppendEnvValues(defaults, overrides []string) []string {
 
 	return defaults
 }
+
+func objectWithLabelArgs(clicontext *cli.Context) (string, map[string]string) {
+	var (
+		namespace    = clicontext.Args().First()
+		labelStrings = clicontext.Args().Tail()
+	)
+
+	return namespace, labelArgs(labelStrings)
+}
+
+func labelArgs(labelStrings []string) map[string]string {
+	labels := make(map[string]string, len(labelStrings))
+	for _, label := range labelStrings {
+		parts := strings.SplitN(label, "=", 2)
+		key := parts[0]
+		value := "true"
+		if len(parts) > 1 {
+			value = parts[1]
+		}
+
+		labels[key] = value
+	}
+
+	return labels
+}