buffer: refactor create buffer

Use createBuffer to reduce new Uint8Array()
and setPrototypeOf.

PR-URL: https://github.com/nodejs/node/pull/4340


Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>