FIX: Use an Array instead of a String to store the java arguments.

Close #4.
To avoid that the JAVA_OPTIONS in /etc/default/jetty keeps growing on each run,you can use the method "uniq" of the Array object each time you add an argument to the list like that the JAVA_OPTIONS in /etc/default/jetty will stop to grow on each run.
e.g: node.set[jetty][java_options] = node.set[jetty][java_options].push(-server).uniq
FIX: Use link that will not expire when the next stable version is released.
NEW: Test new stable release of Jetty 9.
FIX: Use links pointing to Jetty that will not expire when the next stable version is released.