run tests through JES launcher instead of Ant

Before this commit, information about how to launch JES was in each
of the three launchers, plus the build.xml file -- and it took up a
substantial part of build.xml. Now, however, JESstartup has been
configured with a passthrough that allows you to directly access the
Jython shell hidden within.

So, the build.xml file now uses that --jython switch to run the tests,
instead of duplicating all the logic for launching Java.
clean up launchers and add JESEnvironment.{sh,bat} file

To make configuring the JES environmental settings easier, the
launchers now look for a JESEnvironment.sh (or .bat, if on Windows)
file that lives in the same directory as JESConfig.properties.
It will then source before picking a Java and whatnot.

In order to keep the diffs between the three launchers minimal,
I rearranged them a bit so that everything happens in the same order.