Add script to run JDWP tests against prebuilt libjdwp.so

The invocation to run the JDWP tests against the prebuilt/ libjdwp.so
was long and easy to mess up. In order to improve usability we added a
new script that will do it for you.

Bug: 62821960
Test: ./art/tools/run-prebuilt-libjdwp-tests.sh
Change-Id: Idfb9cf19dc50e34fc9ef53ee682ce1c3f86ca178