Implements: blueprint rabbitmq-dns-discovery
Some useful things to note:
1. This uses a StatefulSet instead of a Deployment. The reason for this
is that when RabbitMQ uses DNS for peer discovery, the first thing it
does when trying to join a node is attempt a reverse-dns lookup.
This reverse lookup works when using a StatefulSet, but not a
Deployment.
2. The RabbitMQ configuration was updated to use the new sysctl-style
format. It seems that the new format is required to configure the
new autoclustering features. Additionally, I found that this
generate much clearer error messages than the straight erlang format.
3. I removed the `is-node-properly-clustered` test in the liveness and
readiness probes. This probe isn't directly supported in 3.7.0,
and it wasn't clear that a clustering check was appropriate for each
node.
Change-Id: Ieefbb2205bd77fbac04abcd051fb06fce62e8d97
0982a823e1