Investigate which tests are slower and remove them from commit hooks.

[tejal29]

Internal discussion at:
https://groups.google.com/a/google.com/forum/#!topic/container-tools/AvEPvV63axk

Lets make sure, as i pointed out in the thread, the download_pkgs test is the culprit and move the https://github.com/GoogleCloudPlatform/base-images-docker/blob/master/tests/package_managers/BUILD#L39 to ROOT/integration.
That way we can still keep the commit hook as is.