Port 'docker images' to the engine API

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)

engine/table_test.go

@@ -0,0 +1,28 @@
+package engine
+
+import (
+	"testing"
+	"bytes"
+	"encoding/json"
+)
+
+func TestTableWriteTo(t *testing.T) {
+	table := NewTable("", 0)
+	e := &Env{}
+	e.Set("foo", "bar")
+	table.Add(e)
+	var buf bytes.Buffer
+	if _, err := table.WriteTo(&buf); err != nil {
+		t.Fatal(err)
+	}
+	output := make(map[string]string)
+	if err := json.Unmarshal(buf.Bytes(), &output); err != nil {
+		t.Fatal(err)
+	}
+	if len(output) != 1  {
+		t.Fatalf("Incorrect output: %v", output)
+	}
+	if val, exists := output["foo"]; !exists || val != "bar" {
+		t.Fatalf("Inccorect output: %v", output)
+	}
+}