Fix installation of source feature groups.

Also use qualified version from installation plan so that we can
reliably query features and bundles from the reactor repo in the
case of duplicate IU IDs and as a side effect we don't have to open
jars to get the qualified versions of plugins.

This depends on the patch submitted to xmvn project here:
https://bugzilla.redhat.com/show_bug.cgi?id=1172225