Github user afine commented on the issue:
https://github.com/apache/zookeeper/pull/402
@anmolnar You are correct that the command is executed with argument that
would allow the tests to run in parallel but if you take a look at the
build.xml on branch-3.4 it looks like the code to use "test.junit.threads" is
not there. I believe the JIRA to add this was
https://issues.apache.org/jira/browse/ZOOKEEPER-2183 which shows the change
only touched 3.5 and master.---
