test: run the tests in parallel

This speeds up the whole test time. However, some of the tests are not thread-safe, and that means they might fail. But because now we have separate child processes and a failure repetition mechanism, they can end up passing.

Author: aminya

script/test

@@ -34,7 +34,7 @@ const argv = require('yargs')
   .help().argv;
 
 const assert = require('assert');
-const asyncSeries = require('async/series');
+const asyncParallel = require('async/parallel');
 const childProcess = require('child_process');
 const fs = require('fs-extra');
 const glob = require('glob');
@@ -476,7 +476,7 @@ function requestedTestSuites(platform) {
   return suites;
 }
 
-asyncSeries(testSuitesToRun, function(err, results) {
+asyncParallel(testSuitesToRun, function(err, results) {
   if (err) {
     console.error(err);
     process.exit(1);