fix(@schematics/angular): Use existing universal app if it exists.

Fixes #295

Author: Brocco

packages/schematics/angular/app-shell/index.ts

@@ -66,6 +66,16 @@ function getServerModulePath(host: Tree, app: AppConfig): string | null {
 
 function addUniversalApp(options: AppShellOptions): Rule {
   return (host: Tree, context: SchematicContext) => {
+    const config = getConfig(host);
+    const appConfig = getAppFromConfig(config, options.universalApp);
+
+    if (appConfig && appConfig.platform === 'server') {
+      return host;
+    } else if (appConfig && appConfig.platform !== 'server') {
+      throw new SchematicsException(
+        `Invalid platform for universal app (${options.universalApp}), value must be "server".`);
+    }
+
     // Copy options.
     const universalOptions = {
       ...options,

packages/schematics/angular/app-shell/index_spec.ts

@@ -50,6 +50,23 @@ describe('App Shell Schematic', () => {
     expect(file).toBeDefined();
   });
 
+  it('should use an existing universal app', () => {
+    const universalOptions = {
+      name: defaultOptions.universalApp,
+    };
+
+    let tree: Tree = schematicRunner.runSchematic('universal', universalOptions, appTree);
+    const filePath = '/.angular-cli.json';
+    let content = tree.read(filePath) || new Buffer('');
+    let config = JSON.parse(content.toString());
+    const appCount = config.apps.length;
+
+    tree = schematicRunner.runSchematic('appShell', defaultOptions, tree);
+    content = tree.read(filePath) || new Buffer('');
+    config = JSON.parse(content.toString());
+    expect(config.apps.length).toBe(appCount);
+  });
+
   it('should add app shell configuration', () => {
     const tree = schematicRunner.runSchematic('appShell', defaultOptions, appTree);
     const filePath = '/.angular-cli.json';