Allow JVM_OPTS to be passed to sstablescrub

Can you add a feature request to pass JVM_OPTS to the sstablescrub script – and other places where java is being called? (Among other things, this lets us run java stuff with "-Djava.awt.headless=true" on OS X so that Java processes don't pop up into the foreground – i.e. we have a script that loops over all CFs and runs sstablescrub, and without that flag being passed in the OS X machine becomes pretty much unusable as it keeps switching focus to the java processes as they start.)

— a/resources/cassandra/bin/sstablescrub
+++ b/resources/cassandra/bin/sstablescrub
@@ -70,7 +70,7 @@ if [ "x$MAX_HEAP_SIZE" = "x" ]; then
MAX_HEAP_SIZE="256M"
fi

-$JAVA -ea -cp $CLASSPATH -Xmx$MAX_HEAP_SIZE \
+$JAVA $JVM_OPTS -ea -cp $CLASSPATH -Xmx$MAX_HEAP_SIZE \
-Dlog4j.configuration=log4j-tools.properties \
org.apache.cassandra.tools.StandaloneScrubber "$@"