Repro case:
$ make clean generated_files
$ hack/update-generated-protobuf.sh
This would complain about not finding `fmt`, and it was indicating the wrong
GOROOT. The problem was that the first step built binaries for generating
code, which *embeds* the value of GOROOT into the binary. The whole tree was
bind-mounted into the build container and then JUST the dockerized dir was
mounted over it. The in-container build tried to use the existing binaries,
but GOROOT is wrong.
This change whites-out the whole _output dir.
I first made just an anonymous volume for _output, but docker makes that as
root, which means I can't write to it from our non-root build. So I just put
it in the data container. This seems to work. The biggest change this makes
is that the $GOPATH/bin/ and $GOPATH/pkg/ dirs will persist across dockerized
builds.
This allows us to start building real dependencies into Makefile.
Leave old hack/* scripts in place but advise to use 'make'. There are a few
rules that call things like 'go run' or 'build/*' that I left as-is for now.
aaronxu