Decommission scaleway arm32 systems

[sxa]

Multiple reasons

• They are unreliable
• They are currently running Ubuntu 16.04
• Scaleway have indicated that new image creation will be limited from June 1st
  -- July 1st will be end of support
  -- August 1st will block new C1 instance creations completely, and also BLOCK RESTARTS
  -- September 1 = final end of life - IPs will be detached from the instance

Based on the instability of the scaleway systems and our need to regularly restart them this means an effective absolute end date of August 1st - just over two months from the date I'm opening this issue.

I have already been looking at alternate options, but clearly the preferred one is to get the pis at the colocation setup at Nine fully up and running.

[sxa]

In order to support continuing to build on Ubuntu 16.04 on a replacement system (to hold glibc dependency levels for java 8 and 11) I have been looking at creating a docker environment for running these builds on a more modern host going forward as per https://github.com/adoptium/infrastructure/pull/2201/files

[sxa]

Machines have now had the version of GCC 7.5 updated to resolve the problems described in adoptium/adoptium-support#319
We now also have the ability to build in docker containers as a result of #2201 and have two machines build-equinix-ubuntu1604-armv7l-* set up for this, which should be able to take over the function of the two scaleway build boxes. This just leaves us with the docker one.

[sxa]

Moving this to July as we still have the machines live, but other than for docker they are no longer mandatory in our CI.

[sxa]

IPs have been detached. @sxa's XU4 can handle the docker multiarch job, although that is not likely to be needed at adoptium going forward.