Nameko Release Candidate 2.9.0

Nameko RC 2.9.0 is ready for testing. This is a big one:

   - RPC reply queues are now set to expire rather than auto-delete, and
   are no longer exclusive, allowing clients reconnect.
   - It's now possible to accept messages in multiple serialization
   formats. Adds config-based mechanism for specifying custom serializers.
   - Enhanced environment variable substitution including recursive