chore(build): remove use of q.denodeify

This change also makes webpack properly reject
promise on build errors

Closes #6546

tools/build/webpack/promiseify.js

@@ -0,0 +1,32 @@
+var webpack = require('webpack');
+
+/**
+ * Wraps the original `webpack` function to convert execution
+ * result to a promise and properly report errors.
+ *
+ * @param options
+ * @returns {Function}
+ */
+function webPackPromiseify(options) {
+
+  return new Promise(function (resolve, reject) {
+
+    webpack(options, function(err, stats) {
+      var jsonStats = stats.toJson() || {};
+      var statsErrors = jsonStats.errors || [];
+
+      if (err) {
+        return reject(err);
+      }
+
+      if (statsErrors.length) {
+        return reject(statsErrors);
+      }
+
+      return resolve(stats);
+    });
+
+  });
+}
+
+module.exports  = webPackPromiseify;