cleanup junit tests to eliminate false positives due to "socket reuse" and failure to close client

The junit tests will occasionally fail on hudson due to a few problems:

1) socket in use - sometimes the code/testcode will fail to close a socket, either that or tcp wait
kicks in and the kernel holds onto the socket, either way subsequent tests that use this same
port will fail

2) sometimes the tests fail to close clients, this results in clients attempting to re-connect to
the server started as part of a subsequent test (the timeout is very long). this causes a few
problems, typically extra load on the server or more likely unusual changes to the server that the
next test(s) don't expect. also causes problems when trying to debug the test as the old clients
spew messages into the log.

we see this on hudson, occasionally failures. We also saw this when working on ZOOKEEPER-397, the testng
port. testng does not support "fork mode" for running the tests. as a result all the tests (all) run in a single
vm instance, start to finish. so this problem is exacerbated significantly in that case. this patch only
fixes the problem in junit btw, it does not move to testng