Upgrading flow and fixing lint errors

Summary:
Upgrading to flow 0.91, fixing a bunch of `$FloxFixMe`s that were introduced by upgrading to 0.86.
Also fixing some linting issues.

Reviewed By: priteshrnandgaonkar

Differential Revision: D13900794

fbshipit-source-id: 5d0a1b62371f3b5d34b909bae0876583acb6f977

src/utils/CertificateProvider.js

@@ -8,8 +8,6 @@
 import LogManager from '../fb-stubs/Logger';
 import {RecurringError} from './errors';
 import {promisify} from 'util';
-import child_process from 'child_process';
-const exec = promisify(child_process.exec);
 const fs = require('fs');
 const adb = require('adbkit-fb');
 import {

src/utils/metrics.js

@@ -14,10 +14,10 @@ import {getInstance} from '../fb-stubs/Logger';
 
  Use this variant to report failures in core platform (Flipper) code.
  */
-export function reportPlatformFailures(
-  promise: Promise<*>,
+export function reportPlatformFailures<T>(
+  promise: Promise<T>,
   name: string,
-): Promise<*> {
+): Promise<T> {
   return promise.then(
     fulfilledValue => {
       getInstance().track('success-rate', name, 1);
@@ -37,11 +37,11 @@ export function reportPlatformFailures(
 
  Use this variant to report failures in plugin code.
  */
-export function reportPluginFailures(
-  promise: Promise<*>,
+export function reportPluginFailures<T>(
+  promise: Promise<T>,
   name: string,
   plugin: string,
-): Promise<*> {
+): Promise<T> {
   return promise.then(
     fulfilledValue => {
       getInstance().track('success-rate', name, 1, plugin);