Improve webpack integration

- added gulp build --watch
- updated documentation
- bundle is now loaded after DOMContentLoaded event

Related to blueprint webpack

Change-Id: I04c341987002687efd6713c5296b23e491aacd6f

docs/develop/nailgun/development/env.rst

@@ -279,6 +279,17 @@ Running Nailgun in Fake Mode
 
       gulp dev-server --dev-server-host=127.0.0.1 --dev-server-port=8080 --nailgun-host=127.0.0.1 --nailgun-port=8000
 
+    If you don't want to use a development server but would like to recompile
+    the bundle on any change, use::
+
+      gulp build --watch
+
+    If automatic rebuild on change doesn't work, most likely you need to
+    increase the limit of inotify watches::
+
+      echo 100000 | sudo tee /proc/sys/fs/inotify/max_user_watches
+
+
 Note: Diagnostic Snapshot is not available in a Fake mode.
 
 Running the Fuel System Tests

nailgun/gulpfile.js

@@ -249,10 +249,16 @@ gulp.task('build', function(cb) {
             new webpack.optimize.UglifyJsPlugin({compress: {warnings: false}})
         );
     }
+    if (argv.watch) {
+        config.watch = true;
+    }
 
     rimraf.sync(config.output.path);
 
-    webpack(config).run(function(err, stats) {
+    var compiler = webpack(config);
+    var run = config.watch ? compiler.watch.bind(compiler, config.watchOptions) : compiler.run.bind(compiler);
+
+    run(function(err, stats) {
         if (err) return cb(err);
 
         gutil.log(stats.toString(WEBPACK_STATS_OPTIONS));
@@ -274,7 +280,7 @@ gulp.task('build', function(cb) {
                 .pipe(indexFilter.restore())
                 .pipe(gulp.dest(targetDir))
                 .on('end', cb);
-        } else {
+        } else if (!config.watch) {
             cb();
         }
     });

nailgun/static/index.html

@@ -60,12 +60,14 @@
         }());
 
         if (hasCookies && hasStorage) {
-          loadScript(
-            'static/build/bundle.js?__CACHE_BUST__',
-            'Failed to load compressed Fuel UI bundle. ' +
-            'If you are using development environment, ' +
-            'please run "gulp build" to compile Fuel UI.'
-          );
+          document.addEventListener('DOMContentLoaded', function() {
+            loadScript(
+              'static/build/bundle.js?__CACHE_BUST__',
+              'Failed to load compressed Fuel UI bundle. ' +
+              'If you are using development environment, ' +
+              'please run "gulp build" to compile Fuel UI.'
+            );
+          });
         } else {
           showError('Fuel UI requires Cookies and LocalStorage to work');
         }