[WIP] Upgrading Compose version to 2

[nickdgriffin]

The purpose of this PR is to upgrade the Compose file format version to 2 as version 1 will eventually be deprecated.

This is very much work in progress, I'm raising this early so people know I'm doing it and also for feedback. I'll update the description as I go to indicate where this is.

Some notes for those that read through what I've actually changed:

• This is pretty much just a translation of what we currently have to v2, newer compose features will likely come in future PRs
• I've intentionally gone for an "external" network as we currently create one in the CLI and I didn't want to bite off more than I could chew in this PR - I'll likely change this later in a follow-up PR

Outstanding actions:

• Compose v2 prefixes the volume names, need to check the affects of that
• Double and triple check that nothing has been missed out
• Test it properly - without syslog, with NFS
• Test backwards compatibility and if we need to draw a line under the version of Docker Engine and Compose that we need - looks like at least Docker 1.10.0+ initially
• Remove any commits cherry-picked from my other PRs
• There will probably be some updates to the docs to go with this
• Prepare this PR for actual review

Dependencies:

• Travis: Upgrading Compose to 1.6.2 for bug fixes #128
• Fix: #115 #131
• Changing the --with-stdout behaviour so it works with non-init commands #181

Other comments:

• I've kept the file structure the same as we currently have, but I might collapse etc/volumes/local/default.yml into the main compose file if it can be fully overridden by other types
• If anything gets merged that affects the Compose files whilst I'm working on this it'll likely flag as being unmergable so I'll re-integrate changes as I go
• I'll probably spin off some changes in their own PRs if I think they are of benefit before this is complete

@anton-kasperovich , @SachinKSingh28 , @kramos : I think this might be worthy of becoming 0.4.0 as it's a pretty significant change, what do you think?

[anton-kasperovich]

Yep, i agree that it's major and should be highlighted in separate release, as you mentioned 0.4.0.

For my personal purposes, i've started to work on Compose v3 (not from scratch, i've taken your PR as base). As per "Compose file format compatibility matrix" on a release page https://github.com/docker/compose/releases/tag/1.11.2 It's compatible only with Docker 1.13+ the question here i suppose - do we want to have 2 compose files, like regular docker-compose.yml which will be supported by Docker up to 1.13 and docker-compose.v3.yml which will be supported by Docker 1.13+ ? Ideas?

[nickdgriffin]

Not keen on having to maintain two Compose files as it means duplicating effort going forwards and will also lose the history of one of the two files when, as I assume we will, we go back to just having a single file.

I think in that case I'd rather we maintained a feature branch off master as an "experimental" line, that way when it becomes the normal version we can merge it in to replace the existing file.