[JCLOUDS-189] Upgrade to Karaf 2.3.2. Explicitly specify jclouds feature...

This pull request upgrade to Karaf 2.3.2.
It explicitly specifies the features to be "verified" during build of the feature module.
Finally, it switches to Karaf's pax-exam support which has been moved from openengsb to Karaf as of 2.3.0.