Fix JAR file generation in Java module.
Fix JAR file generation in Java module.

The class file paths must be specified relative to the class files
directory, or the full path starting from / gets embedded in the JAR.

Change-Id: Id33dc5690a3dfa8d4e8619f3f599e408c431de36
Reviewed-by: Christian Kandeler <3aa99dcdd3f0cac61fb81c2a11771c0cc2497607@theqtcompany.com>

villytiger/qbs,qtproject/qt-labs-qbs,Distrotech/qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,villytiger/qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,villytiger/qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,villytiger/qbs,qt-labs/qbs,Distrotech/qbs,villytiger/qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,Distrotech/qbs,gatzka/qt-labs-qbs,Distrotech/qbs,Distrotech/qbs,qt-labs/qbs,gatzka/qt-labs-qbs,qt-labs/qbs,villytiger/qbs,gatzka/qt-labs-qbs,Distrotech/qbs,qtproject/qt-labs-qbs,Distrotech/qbs