The multi-queue no-op I/O scheduler. Does no reordering of requests, minimal overhead. Ideal for fast random I/O devices such as NVME.
Ubuntu 14.04 is EOL and no longer supported. Move up to a later version such as 18.04 LTS which is supported until 2023. The repos for Bionic Beaver will have MySQL 5.7 available so that you can just install it via apt.
Before doing any of this, make sure to dump your databases before doing anything in case something goes awry.
You can also install MySQL 5....