OSGi class loading fixes

  * Changes the way bundles on the classpath are exported to felix - from list of exported packages in system.packages.extra to building extension bundles for each bundle on the classpath. This avoids the case where the same class would be loaded once from the classpath and once from a bundle referenced by a catalog item. When the catalog item tries to install the bundle we see that there is already an existing version installed and use it instead.
  * AggregateClassLoader doesn't relay to parent, using only the explicitly registered classloaders.
  * Force maven-bundle-plugin to include \*.impl.\* and \*.internal.\* packages in the export-package list (referenced between brooklyn bundles)

***NOTE***
Installing all the bundles in brooklyn-dist on my PC takes 3 seconds (once on startup). The slowdown is in Felix itself. Since we will be moving to OSGi based app we will need to load the bundles anyway so I don't see a way out of this.
Agree, better not have the stacktrace in the console, but still I would print the nested exception's message:
log.warn("Unresolved constraint resolving OSGi bundle "+bundleUrlOrNameVersionString+" to load "+type+": "+cause);

Not terribly proud with this code, but couldn't find a better approach to bring out this important cause of ClassNotFoundException.