Upgrade and pin RabbitMQ to 3.8.
Upgrade Erlang to 22 to meet requirements:
https://www.rabbitmq.com/which-erlang.html
Start using bintray repository provided by RabbitMQ.
Linaro builds will be used for aarch64.
Implements: blueprint rabbitmq-version-upgrade
Closes-Bug: #1848452
Change-Id: I3d775fd832f2603181da89009cebc1370a61a023