Also includes other improvements:
- Makefile rule to run tests against remote instance using existing host or image
- Makefile will reuse an instance created from an image if it was not torn down
- Runner starts gce instances in parallel with building source
- Runner uses instance ip instead of hostname so that it doesn't need to resolve
- Runner supports cleaning up files and processes on an instance without stopping / deleting it
- Runner runs tests using `ginkgo` binary to support running tests in parallel
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