osgi, osgi-bundles: trivial fixes

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
osgi-bundles: fix non deterministic build

The Plexus Archiver plugin was sometimes overriding the MANIFEST.MF
generated by the Felix Bundle plugin.
Update the jar plugin configuration to tell it to use the existing
manifest for all OSGI artifacts.

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>