This change updates the Go GN integration to download external
dependencies for Go packages before running "go build". These
dependencies are listed in the pw_go_package template using build
metadata and collected to a "go get" invocation.
To support this, the pw_exec template is expanded to allow setting
positional arguments from a file.
Change-Id: If4f6c71f037b35bb041984da9982a1629d1d36b0
This change renames the pw_test_server module to pw_target_runner and
integrates it into the GN build using the new Go templates. The module
is updated to match the GOPATH structure under its go/ directory, and
its protos are moved into the module protos directory. Additionally,
the simple server and client are split into two separate programs
instead of combining them into one.
Change-Id: I44adeca0989dc7e15cb1a169a6ce183139dde2ce
