WIP: Replace bluebird function usages with native Promise

Created by: pc-jedi

• .return is a short hand by Bluebird. Bluebird .return If the ioredis client is created by the user without using Bluebird Promises the .return function is not available.
• .spread is Bluebird implementation for destructuring an array of promises. Bluebird .spread It can be replaced by ES6 destructuring.
• .timeout Bluebird .timeout
• .map Bluebird .map
• Promise.map replaced by Promise.resolve().map().
• .reduce Bluebird .reduce
• .filter Bluebird .filter
• .each Bluebird .each
• .delay Bluebird .delay
• Promise.delay Bluebird Promise.delay
• .asCallback Bluebird .asCallback
• .reflect Bluebird .reflect
• Promise.promisify Bluebird Promise.promisify
• Promise.method Bluebird Promise.method

Fix #1027 (closed)