Run gapic-generator unit tests in circleCI (#2284)
Run gapic-generator unit tests in circleCI (#2284)

Our TravisCI is failing because of travis-ci/travis-ci#10053, so we should maintain gapic-generator unit test coverage with CircleCI. This can be a temporary patch while we or TravisCI figures out what the deal is.
googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator