Add an option to the bootable JAR to display the Galleon config

There is no way to retrieve the galleon configuration used to generate the bootable JAR. This can be helpful to understand the content of a server. 

The wildfly-jar-maven-plugin, starting 2.0.0.Beta2 adds the provisioning.xml file that reflects the actual config at the root of the JAR. The option --display-galleon-config displays the content of this file.