Duct: investigate classpath extraction

[therealryan]

When we're asked to serve a report using duct, we might have to launch a new instance of it. This means spawning a new JVM with the same classpath as the current one. It's surprisingly difficult to reliably find the current VM's classpath, especially in the context of tests running via maven.

RuntimeMXBean seems to offer direct access to the current classpath - let's take a look at that to see if it's any simpler than the current approach.