1.5 - Make COMPOSE_PROJECT_NAME accessible to environment

Problem

Given that: - containers join the network under their container name - at least for now - container names depends on the project name I think we need a quick basic solution for 1.5 to allow docker-compose with `--x-networking` enabled to work on a project independently from the project name. The reasoning: project names are variable (they can be different for two users depending on their directory, or can be changed in the CLI). So without forcing the project name, when we up a project, we have no way yet to predict the network name - and worse, no way to predict the hostnames of the other containers in the project. Proposed solution I understand that nice solutions are planned for 1.6, but in the mean time I think we need a solution doable for 1.5. I suggest to set and make the environment variable `COMPOSE_PROJECT_NAME` available. This way we can actually predict at which hostname other containers will be accessible in the current network. Something like `${COMPOSE_PROJECT_NAME}_redis_1`. Example What you do now [code block] [code block] Proposal The proposal is to make that possible: [code block] [code block]