title: Rabbitmq-server fails to start if hostname has subdomain
body: <p>Not sure if this is expected but here is what I have found on Ubuntu 16.04. I have named everything via apps and instance count. In example for logstash you have 1.logstash.test.com 2.logstash.test.com 3.logstash.test.com. However rabbitmq-server wont start with that, the hostname cannot have a subdomain name.</p>
  
  <pre><code>Setting up rabbitmq-server (3.5.7-1) ...
  Job for rabbitmq-server.service failed because the control process exited with error code. See "systemctl status rabbitmq-server.service" and "journalctl -xe" for details.
  invoke-rc.d: initscript rabbitmq-server, action "start" failed.
  dpkg: error processing package rabbitmq-server (--configure):
   subprocess installed post-installation script returned error exit status 1
  Processing triggers for systemd (229-4ubuntu7) ...
  Errors were encountered while processing:
   rabbitmq-server
  </code></pre>
  
  <p>When changing the hostname to just logstash.test.com, it works just fine for installing via apt-get. Everything is setup properly in /etc/hosts and /etc/hostname.</p>