Updated Makefile to run the build baclient package for go on the
host instead of as a docker container, to allow the Makefile be
called from another container. Reason being, in a docker-in-docker,
volume mapping requires knowledge of host filesystem path instead
of the docker daemon filesystem path.
Corrected proxy configuration in the scripts to use the USE_PROXY,
PROXY and NO_PROXY environment variables.
Updated Dockerfile to add multi-stage build, to avoid including the
golang-go package in the docker image. Stage one creates the
baclient Go library, and stage two creates the drydock image, and
copies the baclient from stage one image.