Signed-off-by: Pierre Fenoll <pierrefenoll@gmail.com>

Signed-off-by: Pierre Fenoll <pierrefenoll@gmail.com>

Part of #2324.

As an experimental feature for now. To be sure that this value
has the desired effect we may have to tweak the way Ra dependency
is started.

Some ealy tests suggest this works as expected already.

Per discussion with @kjnilsson.

Closes #2354.

When the backend returns an error, we retry.
If we fail to join discovered peers, we also retry.
Schema table sync retries are already in place so nothing
to change there.

Closes #1627.

Pair: @dumbbell.

To override the product name (defaulting to "RabbitMQ"):
* set the `$RABBITMQ_PRODUCT_NAME` environment variable, or
* set the `rabbit` application `product_name` variable.

To override the product version:
* set the `$RABBITMQ_PRODUCT_VERSION` environment variable, or
* set the `rabbit` application `product_version` variable.

To add content to the banner (both the copy logged and the one printed
to stdout), indicate the filename which contains it, à la `/etc/motd`
using:
* the `$RABBITMQ_MOTD_FILE` environment variable, or
* the `rabbit` application `motd_file` variable.

The default motd file is `/etc/rabbitmq/motd` on Unix and
`%APPDATA%\RabbitMQ\motd.txt` on Windows.

Here is an example of the printed banner with name, version & motd
configured:

      ##  ##      WeatherMQ 1.2.3
      ##  ##
      ##########  Copyright (c) 2007-2020 Pivotal Software, Inc.
      ######  ##
      ##########  Licensed under the MPL 1.1. Website: https://rabbitmq.com

      This is an example of a RabbitMQ message of the day.

      The message is written in Paris, France.    \  /
      It is partly cloudy outside, with a       _ /"".-.
      temperature of 12°C. Wind is around         \_(   ).
      30-40 km/h, from south-west.                /(___(__)

      Doc guides: https://rabbitmq.com/documentation.html
      Support:    https://rabbitmq.com/contact.html
      Tutorials:  https://rabbitmq.com/getstarted.html
      Monitoring: https://rabbitmq.com/monitoring.html

      Logs: /tmp/rabbitmq-test-instances/rabbit/log/rabbit@cassini.log
            /tmp/rabbitmq-test-instances/rabbit/log/rabbit@cassini_upgrade.log

      Config file(s): /tmp/rabbitmq-test-instances/test.config

      Starting broker... completed with 0 plugins.

New APIS are available to query those product informations and use them
in e.g. plugins such as the management API/UI:
* rabbit:product_info/0
* rabbit:product_name/0
* rabbit:product_version/0
* rabbit:motd_file/0
* rabbit:motd/0

[#170054940]

References #2182, rabbitmq/rabbitmq-common#343.

Extract rabbit_definitions from rabbitmq-management