Make karaf osgi-sample extract to target directory #3216

The osgi-sample now extracts files to the local target directory instead of the HOME/.pax directory.
The test is now optional as well, and needs to be enabled with the flag `-Dakka.osgi.sample.test=true`.

The jenkins jobs on jenkins.akka.io and jenkins.typesafe.com have been updated with the flag.

There is still a problem with mvn pulling down published SNAPSHOTS and not using the locally built stuff,
but that's in this ticket https://www.assembla.com/spaces/akka/tickets/3224, since we need to stop spurious
build failures.