Make dtest rule constructor to use default helper and make the dtest helper to know default rmi port

This is an idea of few enhancements in the dtest library.

• if app want to use the dtest library as it opens rmi port now it enforce application to define system property org.jboss.byteman.contrib.dtest.rmiregistry.port but it's normally defined as 1099 (Instrumentor creation knows so), that should be defaulted for the helper too. It's quite tedious to need to define it even when want to use the default version.
• rule constructor should offer way to install rule directly in its methods