Skeleton implementation of L3 using PipelineOrchestration

This refactors the L3 interface to fit the static pipeline model

L3 logic stays in net-virt and the service tables in net-virt-providers
implement the new interfaces. The logic in net-virt can resolve the
implementation of these interfaces through the OSGi SR.

Ideally service lookup should not be handled in the net-virt Activator,
instead we should allow the OFXProvider classes to handle this by
watching for implementations of AbstractServiceInstance with a service
property that matches their name.

Change-Id: I0e41d992e0ff1d8de2d25b02ce8e5a36e27e6ae7
Signed-off-by: Dave Tucker <djt@redhat.com>