Add Dockerfile that will build using go 1.9.3.
Add Dockerfile that will build using go 1.9.3.

It also gets the testing utilities that the go test script
uses.  This speeds up testing locally b/c it doesn't have to
do this every time.

dcos/dcos-metrics,dcos/dcos-metrics,dcos/dcos-metrics,dcos/dcos-metrics,dcos/dcos-metrics