auto-add code coverage reporter

Author: filipesilva

packages/@angular/cli/plugins/karma.ts

@@ -114,6 +114,12 @@ const init: any = (config: any, emitter: any, customFileHandlers: any) => {
     }
   });
 
+  // When using code-coverage, auto-add coverage-istanbul.
+  config.reporters = config.reporters || [];
+  if (testConfig.codeCoverage && config.reporters.indexOf('coverage-istanbul') === -1) {
+    config.reporters.push('coverage-istanbul');
+  }
+
   // Our custom context and debug files list the webpack bundles directly instead of using
   // the karma files array.
   config.customContextFile = `${__dirname}/karma-context.html`;