Add integration test with Webpack

To verify that driver can be used in a browser app. This makes sure no
NodeJS APIs are used unconditionally. Webpack build fails for such
APIs at compile time. Webpack uses "browser" field from package.json to
replace Node components with browser components. All environment-dependent
code should only be exposed from `node/index.js` and `browser/index.js`.

Author: lutovich

gulpfile.babel.js

@@ -38,7 +38,6 @@ var path = require('path');
 var minimist = require('minimist');
 var cucumber = require('gulp-cucumber');
 var install = require("gulp-install");
-var os = require('os');
 var file = require('gulp-file');
 var semver = require('semver');
 var sharedNeo4j = require('./test/internal/shared-neo4j').default;
@@ -138,13 +137,14 @@ gulp.task('all', function(cb){
 
 // prepares directory for package.test.js
 gulp.task('install-driver-into-sandbox', ['nodejs'], function(){
-  var testDir = path.join(os.tmpdir(), 'sandbox');
+  var testDir = path.join('build', 'sandbox');
   fs.emptyDirSync(testDir);
 
   var packageJsonContent = JSON.stringify({
-      "dependencies":{
-          "neo4j-driver" : __dirname
-      }
+    'private': true,
+    'dependencies': {
+      'neo4j-driver': __dirname
+    }
   });
 
   return file('package.json', packageJsonContent, {src:true})