Add additional error handling to Python installation for Notebooks (#4891)

* Also enabled integration tests for python installation.

extensions/notebook/src/test/index.ts

@@ -2,8 +2,6 @@
  *  Copyright (c) Microsoft Corporation. All rights reserved.
  *  Licensed under the Source EULA. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
-// import * as vscode from 'vscode';
-// import { context } from './testContext';
 
 const path = require('path');
 const testRunner = require('vscode/lib/testrunner');