Sometimes when drainer starts it gets short hostname rather than full and can't join cluster

The first time the drainer pod spun up when testing the changes for ENTMQBR-2825 I saw that the drainer pod log was showing

2019-09-11 16:48:21,525 ERROR [org.apache.activemq.artemis.core.client] AMQ214033: Cannot resolve host : java.net.UnknownHostException: ex-aao-ss-1

in multiple locations and also this telling line

2019-09-11 16:48:21,011 INFO  [org.apache.activemq.artemis.core.server] AMQ221020: Started EPOLL Acceptor at ex-aao-ss-2:61616 for protocols [CORE]

However, once I scaled up a broker pod then scaled back down again I saw instead a drainer pod log with no UnknownHost exceptions and saw this telling line:

2019-09-11 16:52:34,936 INFO  [org.apache.activemq.artemis.core.server] AMQ221020: Started EPOLL Acceptor at ex-aao-ss-2.amq-broker-amq-headless.aao-demo-0.svc.cluster.local:61616 for protocols [CORE]

There were no changes between the first scaledown and the subsequent scale up and scale down. Also note that the logs attached show zero messages migrated as there were no messages in the journals of the brokers.

It's possible this is a local environment DNS issues but this would need to be verified.