GO: Be able to build from sub directory

[clarsonneur]

Module : GO

After build_env script executed, the build environment gets loaded, and go and glide became available.

When you are in project root, go start docker from the project root.
But if we move to a subdirectory, docker stay in the same working directory. But sometimes, we just need a simple module build and not all the application build.

Ex:
Following looks good:

[/home/larsonsh/src/forj/src/forjj] $ go build
++ sudo docker run --rm -i -t -v /home/me/src/forj/:/go -w /go/src/forjj -u 10001 forjj-go-env /usr/local/go/bin/go-static build -ldflags '-X main.build_branch=workspace-mgt -X main.build_commit=6ac25087d1fc45d4662d082943068129e4712f55 -X main.build_date=2018-09-06_22:18:07_+0200 -X main.build_tag=false'

Following do not looks good:

[/home/larsonsh/src/forj/src/forjj/workspace] $ go build
++ sudo docker run --rm -i -t -v /home/me/src/forj/:/go -w /go/src/forjj -u 10001 forjj-go-env /usr/local/go/bin/go-static build -ldflags '-X main.build_branch=workspace-mgt -X main.build_commit=6ac25087d1fc45d4662d082943068129e4712f55 -X main.build_date=2018-09-06_22:18:07_+0200 -X main.build_tag=false'

This last sentence build from the project root and not from project root/workspace

Requires to build only the sub-directory.

[clarsonneur]

With go, we could build like go build forjj_modules/cli. Do considering this use case differently.