Fake being in GOPATH when generating code.

[porridge]

What this PR does / why we need it:

This is a workaround for the code generators requiring $GOPATH to put output in the correct location.
Details in the issue.

Fixes #1252

[ANeumann82]

I ran into the same issue (currently working on multiple api version, and conversion-gen, etc).
I've solved it with something like this:

if [[ -d ${CODE_GEN_DIR} ]]; then
    echo "Using cached code generator version: $VERSION"
else
    git clone https://github.com/kubernetes/code-generator.git "${CODE_GEN_DIR}"
    git -C "${CODE_GEN_DIR}" reset --hard "${VERSION}"
    (
        cd "${CODE_GEN_DIR}"
        # Make sure code-gen uses the local kudo codebase, and not a remote module
        go mod edit -replace=github.com/kudobuilder/kudo=../../../
    )
fi

in the update_code_gen.sh.

This looks a bit easier than faking the gopath, but maybe I have overlooked something?

[ANeumann82]

Mmmmm, this might fix a different issue than the one I mentioned in my previous comment. In my case the issue was that the codegens used a go module of kudo to analyze the code and generate stuff.