gitignored file in repo

The file `Dockerfile.test` is covered by the `*.test` in the `.gitignore` file.  This causes issues when using `go dep`, as it imports the repo but git ignores that file, leading to it not being vendored.

Fixes:
 * rename `Dockerfile.test` to something that isn't ignored (e.g., `test-Dockerfile`)
 * adjust the `.gitignore` to not ignore this file