Test: write heap dump per default

The heap dump is always interesting in case a test causes an OOM.
Per default is is written to target/JX/pidXYZ.hprof

pom.xml

@@ -475,6 +475,7 @@
                                 <param>-XX:MaxPermSize=128m</param>
                                 <param>-XX:MaxDirectMemorySize=512m</param>
                                 <param>-Des.logger.prefix=</param>
+                                <param>-XX:+HeapDumpOnOutOfMemoryError</param>
                             </jvmArgs>
                             <shuffleOnSlave>${tests.shuffle}</shuffleOnSlave>
                             <sysouts>${tests.verbose}</sysouts>