Elsy Templates Incompatible with Docker-Compose File Format 2.1 and Beyond

[paulcichonski]

We support the v2 docker-compose file format, but when you try to use anything beyond that (e.g., 2.1) in your repo lc bootstrap will fail with:

ERROR: Version mismatch: file /<somepath>/lc_docker_compose_template155327358 specifies version 2.0 but extension file ./docker-compose.yml uses version 2.1

This is because we hardcode version "2.0" in the template definitions, and then are not smart about dealing with minor versions. Example: https://github.com/cisco/elsy/blob/master/template/mvn.go#L79.