Use conf.d to enable console logging in RMQ 3.9+

[lukebakken]

This replaces the RABBITMQ_LOGS=- env variable.

Fixes #554

Test procedure is documented here:

https://github.com/lukebakken/test-docker-library-rabbitmq-gh-554

[michaelklishin]

I tested an image built from this branch and logging works as expected,

[michaelklishin]

@lukebakken has an example repo with some instructions: https://github.com/lukebakken/test-docker-library-rabbitmq-gh-554

[tianon]

Do you think it'd be reasonable for us to combine these two config files into a 00-docker-defaults.conf or even 10-docker-defaults.conf (so users can inject either before or after without too much hassle), or do you think having these separate like this is better?

[lukebakken]

@tianon great question. I only added a new file because of the comment in the existing one:

https://github.com/docker-library/rabbitmq/blob/master/10-default-guest-user.conf#L1-L3

I'll modify the PR to combine the files into 10-defaults.conf. I will add a note about log.console being necessary if you want to see logs the "usual" way in a container.

[michaelklishin]

I like the idea of combining them. Why would anyone add a file before these defaults, though? Aren't defaults meant to be overridden? ;) anyhow, 10-defaults.conf SGTM.

[lukebakken]

@tianon thanks for your quick reviews.

[lukebakken]

I just read through #506 and this PR does not seem to introduce a situation like the one described there, thankfully.

[michaelklishin]

@tianon is there anything else we should do to get this in? :)

[tianon]

Sorry, just patience 🙈

Thanks! ❤️