node.name environment variable

[mscreations]

EMQX documentation shows that the environment variable to be set for node.name should be EMQX_NODE__NAME (two underscores), but docker-entrypoint.sh only honors setting the node.name with EMQX_NODE_NAME (one underscore).

I also was confused like #44 because the Github link from the documentation takes you to the other emqx package source. I'm not sure which one I should be using emqx or emqx/emqx. Docs say emqx. Extremely confusing.