rabbitmq: make all dependencies explicit

Some things were provided by default, some by systemd unit and some
were just miraculously working. This turns them into explicit
dependencies of the package itself, making everything properly
overrideable.

+ providing glibcLocales fixes elixir compile warnings

+ providing systemd dependency allows rabbit to use systemctl for unit
  activation check instead of falling back to sleep. This was seen as
  a warning during startup.