Refactor manifests generation

- introduce manifestgen pkg, to be consumed by the CLI and Terraform provider
- consolidate defaults in manifestgen/install pkg
- introduce Manifest as the returning type of manifest generation
- add helper function to Manifest for writing multi-doc YAMLs on disk

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

pkg/manifestgen/install/install_test.go

@@ -0,0 +1,40 @@
+/*
+Copyright 2020 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package install
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+)
+
+func TestGenerate(t *testing.T) {
+	opts := MakeDefaultOptions()
+	output, err := Generate(opts)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, component := range opts.Components {
+		img := fmt.Sprintf("%s/%s", opts.Registry, component)
+		if !strings.Contains(output.Content, img) {
+			t.Errorf("component image '%s' not found", img)
+		}
+	}
+
+	fmt.Println(output)
+}