Description:
When installing/upgrading rabbitmq more than one time, the /etc/rabbitmq/rabbitmq-env.conf is badly patched.

The problem comes from the line "NODENAME=rabbit" which is changed to add the @hostname.
NODENAME=rabbit -> NODENAME=rabbit@hostname

However, when the file is already there with the correct hostname, another installation adds again the hostname:
NODENAME=rabbit@hostname -> NODENAME=rabbit@hostname@hostname

This is annoying as I always have to check this file, each time I want to use rabbitmq (since rabbitmq fails to start because of this).
sudo journalctl -u rabbitmq
juin 22 10:08:52 arch-jp systemd[1]: Started RabbitMQ Messaging Server.
juin 22 10:08:53 arch-jp rabbitmq[675]: ERROR: epmd error for host arch-jp@arch-jp@arch-jp@arch-jp: nxdomain (non-existing domain)
juin 22 10:08:53 arch-jp systemd[1]: rabbitmq.service: Main process exited, code=exited, status=1/FAILURE
juin 22 10:08:54 arch-jp rabbitmq[827]: Stopping and halting node 'rabbit@arch-jp@arch-jp@arch-jp@arch-jp' ...
juin 22 10:08:54 arch-jp rabbitmq[827]: Error: unable to connect to node 'rabbit@arch-jp@arch-jp@arch-jp@arch-jp': nodedown
juin 22 10:08:54 arch-jp rabbitmq[827]: DIAGNOSTICS
juin 22 10:08:54 arch-jp rabbitmq[827]: ===========
juin 22 10:08:54 arch-jp systemd[1]: rabbitmq.service: Unit entered failed state.
juin 22 10:08:54 arch-jp systemd[1]: rabbitmq.service: Failed with result 'exit-code'.

I already found where and how to solve this.
=> https://git.archlinux.org/svntogit/community.git/tree/trunk/rabbitmq.install?h=packages/rabbitmq line 7.

I added the patch in attachment.

Additional info:
* package version(s)
rabbitmq 3.6.9-2 (but I noticed the issue since more than a year)