Add missing hostname to nodename in RabbitMQ for multinode deployment

When a RabbitMQ node in multiple RabbitMQ nodes is started during
multinode deployment, it is required to communicate with each other
to be clustered. However, RabbitMQ nodes cannot communicate between
them due to missing host name in the nodename environment variable
of RabbitMQ. Subsequently, all of RabbitMQs cannot be started and
it will give rise to a deployment failure.

Change-Id: I7b4ba76807750db4a14d859454ba650bdaaf23ca
Signed-off-by: Taeha Kim <kthguru@gmail.com>

ansible/roles/rabbitmq/templates/rabbitmq-env.conf.j2

-RABBITMQ_NODENAME=rabbit
+RABBITMQ_NODENAME=rabbit@{{ ansible_hostname }}
 RABBITMQ_BOOT_MODULE=rabbit_clusterer
 RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS="-pa /usr/lib/rabbitmq/lib/{{ rabbitmq_version }}"