chore: minor Flow fixes

.eslintrc.js

@@ -4,6 +4,7 @@ module.exports = {
     __DEV__: true,
     $Dict: true,
     $Diff: true,
+    $ElementType: true,
     $Exact: true,
     $Keys: true,
     $PropertyType: true,

@xen-orchestra/fs/src/abstract.js

@@ -1,5 +1,6 @@
 // @flow
 
+// $FlowFixMe
 import getStream from 'get-stream'
 import { randomBytes } from 'crypto'
 import { fromCallback, fromEvent, ignoreErrors, timeout } from 'promise-toolbox'

@xen-orchestra/fs/src/checksum.js

@@ -1,6 +1,5 @@
 // @flow
 
-// $FlowFixMe
 import through2 from 'through2'
 import { createHash } from 'crypto'
 import { defer, fromEvent } from 'promise-toolbox'

packages/xo-server/src/size-stream.js

@@ -1,6 +1,5 @@
 // @flow
 
-// $FlowFixMe
 import through2 from 'through2'
 import { type Readable } from 'stream'
 

packages/xo-server/src/xo-mixins/backups-ng/index.js

@@ -147,12 +147,12 @@ const defaultSettings: Settings = {
   timeout: 0,
   vmTimeout: 0,
 }
-const getSetting = <T>(
+const getSetting = <T, K: $Keys<Settings>>(
   settings: $Dict<Settings>,
-  name: $Keys<Settings>,
+  name: K,
   keys: string[],
   defaultValue?: T
-): T | any => {
+): T | $ElementType<Settings, K> => {
   for (let i = 0, n = keys.length; i < n; ++i) {
     const objectSettings = settings[keys[i]]
     if (objectSettings !== undefined) {

packages/xo-server/src/xo-mixins/workers/worker.js

@@ -5,8 +5,11 @@ import { mergeVhd as mergeVhd_ } from 'vhd-lib'
 
 // Use Bluebird for all promises as it provides better performance and
 // less memory usage.
+//
+// $FlowFixMe
 global.Promise = require('bluebird')
 
+// $FlowFixMe
 const config: Object = JSON.parse(process.env.XO_CONFIG)
 
 export function mergeVhd (