Fix go build process to actaully use customizes env variables

build/backend.js

@@ -66,8 +66,6 @@ gulp.task('backend:prod', ['package-backend-source'], function(doneFn) {
                 doneFn, {
                   // Disable cgo package. Required to run on scratch docker image.
                   CGO_ENABLED: '0',
-                  // Scratch docker image is linux.
-                  GOOS: 'linux',
                 });
           },
           function(error) { doneFn(error); });

build/gocommand.js

@@ -44,9 +44,13 @@ const minGoVersion = '1.5.0';
  *
  * @param {!Array<string>} args - Arguments of the go command.
  * @param {function(?Error=)} doneFn - Callback.
+ * @param {!Object<string, string>=} [envOverride] optional environment variables overrides map.
  */
-export default function spawnGoProcess(args, doneFn) {
-  checkPrerequisites().then(() => spawnProcess(args)).then(doneFn).fail((error) => doneFn(error));
+export default function spawnGoProcess(args, doneFn, envOverride) {
+  checkPrerequisites()
+      .then(() => spawnProcess(args, envOverride))
+      .then(doneFn)
+      .fail((error) => doneFn(error));
 }
 
 /**
@@ -146,12 +150,14 @@ function checkGodep() {
  * Promises an error if the go command process fails.
  *
  * @param {!Array<string>} args - Arguments of the go command.
+ * @param {!Object<string, string>=} [envOverride] optional environment variables overrides map.
  * @return {Q.Promise} A promise object.
  */
-function spawnProcess(args) {
+function spawnProcess(args, envOverride) {
   let deferred = q.defer();
+  let envLocal = lodash.merge(env, envOverride);
   let goTask = child.spawn('godep', ['go'].concat(args), {
-    env: env,
+    env: envLocal,
     stdio: 'inherit',
   });
   // Call Gulp callback on task exit. This has to be done to make Gulp dependency management