Permit non-loopback guest access to Rabbit.

Recent versions of RabbitMQ have defaulted to only permitting the guest
user to connect from the loopback address.

Many elements have yet to consume rabbit accounts - until the configuration
of per-service (or per-server) accounts is finalised, ensure that newer
rabbit versions will be backwardly-compatible with the old behaviour.

Change-Id: I30e0156862c5672aef3e31a6919c8fe1957e3a02
Related-bug: #1315474
Related-bug: #1317778
Merge "Permit non-loopback guest access to Rabbit."