CHEF-4346 run rabbitmq on non-default port

This PR changes the port on which rabbitmq will run from the default rabbitmq 5672 to 8672. The patch set also includes a cleanup of the postgresql recipe to allow reconfigure to run when all services are stopped. This is important because changing the rabbitmq service port would best be done as:

```
chef-server-ctl stop
# edit /etc/chef-server/chef-server.rb
chef-server-ctl reconfigure
chef-server-ctl start
```