ZooKeeper flakey tests and some Jenkins updates.

[Patrick Hunt <ph...@apache.org>]

Hi folks. Michael Han setup a ZK flakey test dashboard some time ago which
I've found very useful to understand the quality of the various branches.
https://builds.apache.org/job/ZooKeeper-Find-Flaky-Tests/lastSuccessfulBuild/artifact/report.html

I noticed recently that changes in the Jenkins infrastructure has been
causing some of our tests to fail consistently (config issues). I've taken
a pass through and tried to clean some of this up. One thing to note is
that openjdk seems to be having an issue from and env perspective (unless I
just can't figure out the right config setting...) see
https://issues.apache.org/jira/browse/INFRA-15175

Additionally with java9 reaching GA I'm sure more users will want to start
taking this up. We have a trunk based build which I cleaned up however we
are missing 3.5/3.4 jobs. I'm working on adding these.

Patrick