Github user tillrohrmann commented on the issue:
https://github.com/apache/flink/pull/6352
The failing test case seems to be caused by
`YARNSessionFIFOITCase#testJavaAPI` not calling `yarnCluster.shutdownCluster`.
I've fixed this problem in master and the release branch. Rebasing onto the
latest master should hopefully give a green Travis build.---
