Convert some CommonJS constructs to ES6

Summary:
Tried to automate this with [cjs-to-es6](https://github.com/nolanlawson/cjs-to-es6) but it only
works on vanilla JS files without any special Flow syntax. I converted some places
manually but we can just do the rest as we modify the files.

Reviewed By: jknoxville

Differential Revision: D16340187

fbshipit-source-id: b55c7ce2d719876e47e85f5f3fce13b8c8ae4010

src/utils/CertificateProvider.js

@@ -8,13 +8,13 @@
 import type {Logger} from '../fb-interfaces/Logger';
 import Server from '../server';
 import {promisify} from 'util';
-const fs = require('fs');
+import fs from 'fs';
 import {
   openssl,
   isInstalled as opensslInstalled,
 } from './openssl-wrapper-with-promises';
-const path = require('path');
-const tmp = require('tmp');
+import path from 'path';
+import tmp from 'tmp';
 const tmpFile = promisify(tmp.file);
 const tmpDir = promisify(tmp.dir);
 import iosUtil from '../fb-stubs/iOSContainerUtility';

src/utils/info.js

@@ -5,7 +5,7 @@
  * @format
  */
 
-const os = require('os');
+import os from 'os';
 
 export type Info = {
   arch: string,

src/utils/openssl-wrapper-with-promises.js

@@ -6,7 +6,7 @@
  */
 
 import {exec as opensslWithCallback} from 'openssl-wrapper';
-const child_process = require('child_process');
+import child_process from 'child_process';
 
 export function openssl(action: string, options: {}): Promise<string> {
   return new Promise((resolve, reject) => {