Allow to set User/pass via env var

[moimael]

Hi,

First thanks for this docker image, really made my day !

Right now i'm forced to create a volume containing rabbitmq.config to change default rabbitmq user/pass (which cannot stay guest/guest in any production environment).

So i was wondering if this image could natively integrate the possibility of setting them via docker env var ? I saw some third party rabbit images doing so.

What do you think ?

[yosifkit]

There was some discussion in #12, but I never saw a PR for it 😞.

[moimael]

There are 2 PR for this, any ETA ? :)