Temurin-build: Add openjdk10 aarch64 builds to the pipelines

[sxa]

As discussed with @smlambert in #build on slack the builds at https://ci.adoptopenjdk.net/job/openjdk10_build_arm64_linux/ aren't being run regularly via the pipelines and are not publishing so there are no regular nightlies popping up

[gdams]

should just be a case of adding some code to https://github.com/AdoptOpenJDK/openjdk-build/blob/master/pipelines/openjdk10_nightly_pipeline.groovy#L3-L10

[smlambert]

I'll add this line:
buildMaps['arm64'] = [test:['openjdktest'], ArchOSs:'arm64_linux']

[vielmetti]

Thanks for looking at this.