Fix project setup of uitests/org.openjdk.jmc.test.jemmy

uitests/org.openjdk.jmc.test.jemmy is a plugin project which is no test-project itself but an auxiliary library to other uitests.

Currently, the sources reside in the src/test/java folder and the eclipse configuration would also place the compiled classes in target/test-classes. When one does a plain maven build, without Eclipse involvement or using the clean target, everything works fine since then the compiled classes are generated into target/classes. However, building the project in eclipse generates the classes in target/test-classes and this causes the surefire plugin to pick up some classes as potential tests. Since the test.jemmy project is not configured for launching a test runtime, we then see failures.