[golang] Support of V2 package of go lib

[frozeNinK]

for example
if a package, like urfave cli v2 is to be used in a project, pants seems to try to find it in

/home/<user-name>/repos/<repo-name>/.pants.d/resolve/go/e77e8d8d0448/3rdparty.go.github.com.urfave.cli.v2/current/gopath/src/github.com/urfave/cli

instead of

/home/<user-name>/repos/<repo-name>/pants.d/resolve/go/e77e8d8d0448/3rdparty.go.github.com.urfave.cli.v2/current/gopath/src/github.com/urfave/cli/v2

ref: https://blog.golang.org/versioning-proposal

[Eric-Arellano]

We recently decided to focus our energy on the release of Pants 2.0, which only works with the new v2 engine.

This means that Pants 2.0 will not support Go at first, as we're initially focused on a stellar Python experience. Users may continue to use the Pants 1.x plugin. We also plan to rebuild Go support from the ground-up in the future (timeline will determined by user interest).

I'm closing this as we, unfortunately, won't likely get to fixing it in Pants 1.x. Please feel free to reopen if anyone is interested in implementing the change in Pants 1.x - we can give some guidance.