Arm64v8 update (i.e. for Raspberry Pi 3 clusters)

[ikluft]

[This is resubmitting pull request #111 from July in its own "arm64v8-update" branch, and current updates. Since the original PR didn't go in as quickly as I thought it would, it needed its own branch to keep it up to date.]

The reason for this PR is because the "Dockerfile.aarch64" is based on aarch64/node:4.6.0-slim which is marked as deprecated on its description, both for the aarch64 architecture (replaced by arm64v8) and severely out-of-date node 4.6 from 2016 with unreliable backward-compatibility support in current npms. Let's update this to catch up with the Dockerfile in the same directory.

I'm submitting changes I made to get the Swarm Visualizer to work on a Raspberry Pi 3 cluster. Docker's docs say the aarch64 architecture is deprecated in favor of arm64v8. Also, the old Dockerfile.aarch64 hasn't kept up with changes to the primary Dockerfile, which when applied reduced the image size from 341MB to 157MB.

The changes in this PR are: 1) rename Dockerfile.aarch64 to Dockerfile.arm64v8, 2) update Dockerfile.arm64v8 with changes that have been made to Dockerfile, 3) update the README.md to describe this option for ARM64. A change since July is that it now uses node 8.12 instead of 8.11 to pick up current security patches.

I have a build of this available at https://hub.docker.com/r/ikluft/visualizer-arm64v8/

[StefanScherer]

If we merge #105 this PR is obsolete.

When you look at the multi-arch node alpine image you see that the base image supports ARMv6 for RPi Zero/1 as well as arm64 for RPi 3 64bit.

$ docker run --rm mplatform/mquery node:8-alpine
Unable to find image 'mplatform/mquery:latest' locally
latest: Pulling from mplatform/mquery
db6020507de3: Pull complete 
f11a2bcbeb86: Pull complete 
Digest: sha256:e15189e3d6fbcee8a6ad2ef04c1ec80420ab0fdcf0d70408c0e914af80dfb107
Status: Downloaded newer image for mplatform/mquery:latest
Image: node:8-alpine
 * Manifest List: Yes
 * Supported platforms:
   - linux/amd64
   - linux/arm/v6
   - linux/arm64
   - linux/386
   - linux/ppc64le
   - linux/s390x

So everyone on ARM can just use the Dockerfile without the need of special Dockerfile.arm* files.

[ManoMarks]

Made obsolete by #105