fix(@angular-devkit/build-angular): fixed ignoring of karma plugins c…

…onfig

Previously `karma-coverage` was validated only when in karma plugins config one of these was added
``'karma-coverage'` or `require('karma-coverage')`

This change will allow cli to validate `karma-coverage` plugin if in `karma.conf.js` `'karma-*'` is used. Example:
```
plugins: [
      ...
      'karma-*',
      require('@angular-devkit/build-angular/plugins/karma'),
      ...
    ]
```

Fixes angular#19993

packages/angular_devkit/build_angular/src/karma/code-coverage_spec.ts

@@ -184,4 +184,16 @@ describe('Karma Builder code coverage', () => {
     expect(success).toBe(true);
     await run.stop();
   }, 120000);
+
+  it('is able to process coverage plugins provided as string karma-*', async () => {
+    host.replaceInFile('karma.conf.js', /plugins: \[.+?\]/s, `plugins: [
+      'karma-*',
+      require('@angular-devkit/build-angular/plugins/karma'),
+    ]`);
+    const run = await architect.scheduleTarget(karmaTargetSpec, { codeCoverage: true });
+
+    const {success} = await run.result;
+    expect(success).toBe(true);
+    await run.stop();
+  }, 120000);
 });

packages/angular_devkit/build_angular/src/webpack/plugins/karma/karma.ts

@@ -7,10 +7,13 @@
  */
 // tslint:disable
 // TODO: cleanup this file, it's copied as is from Angular CLI.
+import * as fs from 'fs';
 import * as http from 'http';
 import * as path from 'path';
 import * as glob from 'glob';
 import * as webpack from 'webpack';
+
+const karmaPath = path.dirname(require.resolve('karma'));
 const webpackDevMiddleware = require('webpack-dev-middleware');
 
 import { KarmaWebpackFailureCb } from './karma-webpack-failure-cb';
@@ -336,6 +339,13 @@ function fallbackMiddleware() {
 function isPlugin(moduleId: string, pluginName: string) {
   return (plugin: string|{}): boolean => {
     if (typeof plugin === 'string') {
+      if(karmaPath) {
+        const pluginDirectory = path.join(karmaPath, '../../');
+        const regexp = new RegExp(`^${plugin.replace('*', '.*')}`)
+        const installeKarmaPlugins = fs.readdirSync(pluginDirectory)
+        .filter((installedPluginName) =>  regexp.test(installedPluginName));
+        return installeKarmaPlugins.includes( moduleId);
+      }
       return plugin === moduleId;
     }
     return pluginName in plugin;