Don't require $GOPATH to be set

[briansmith]

When running docker-compose run boulder ./test.sh (or anything) when $GOPATH isn't set, I get this cryptic error:

ERROR: Cannot create container for service boulder: create .: volume name is too short, names should be at least two alphanumeric characters

As of Go 1.8, the default $GOPATH is $HOME/go so requiring $GOPATH to be explicitly set will be increasingly confusing to people. This was something that tripped me up when I first started working on Boulder.

[briansmith]

Here's the Go 1.8 issue describing the default $GOPATH: golang/go#17262

[jsha]

Good catch, thanks. And this is something that I think has caught a number of people.

This may be tricky to implement, however. Right now we rely on these two lines in docker-compose.yml:

    volumes:
      - $GOPATH:/go/

This doesn't really support if/else statements. And I think the plan is to actually deprecate variable interpolation in future Docker versions. So we need to figure out what the best practice is for mounting a path that's usually in someone's homedir into a docker volume (with docker compose).