(PE-2650) rack environment setup improvement

This patch improves the setup of the jruby-rack environment
resulting in less friction when running a rack app from a
jar file.
(PE-2650) update tests/examples

This patch updates the examples and tests contained in this project
for the new trapperkeeper defservice syntax and also makes sure
that the example rack applications are on the classpath so that they
can be found by the add-rack-handler function provided by this project.