Clustering: Dynamically load different RoutingLogic implementations based on installed karaf features

For the Unified Secure Channel (USC) Project (https://wiki.opendaylight.org/view/USC:Main) in Lithium, there may need to be a mechanism for the controller to dynamically load an alternative RoutingLogic implementation based on whether the USC karaf feature is installed.

Implementation details TBD.

There may be some commonality between this requirement and the requirements from OpenFlow's device mastership concept, e.g. always route RPC calls to the device master.