Cargo plugin expects to be executed from inside .jar

Currently cargo plugin can't be used with m2eclipse workspace resolution. That is having the project open on Eclipse workspace while some other project utilizes it. This would give advantage of hot code replacement but currently plugin execution stops when cargo checks core container availability. Version for the core container is pulled out of package info that is available only when execution happens from inside of a jar and in this scenario all of the plugin class files reside in a directory.

Here's a patch that utilizes maven project directly instead of round tripping via 'Implementation-Version' from jar manifest