Maven repo 403 again

Similar to Continuous maven repo 403, we are seeing maven 403 again continuously.

E.g. https://travis-ci.org/pantsbuild/pants/jobs/611649098#L1424

E         pants.net.http.fetcher.Fetcher.PermanentError: Fetch of https://repo1.maven.org/maven2/org/apache/ivy/ivy/2.4.0/ivy-2.4.0.jar failed with status code 403

This appears to be a false alarm. We suspect the issue is actually between Pants’s use of Google Remote Build Execution (RBE) and Maven. We could not reproduce the issue when running all of our tests locally through Travis without Google RBE.