Fix blueprint assumptions around odl:rpc-service

The odl:rpc-service extension makes assumptions about RPC lifecycle which are not strictly true when the definition is translated to DOMRpcIdentifier, most notably about when an RPC implementation is registered.

Current codebase happens to work due to how sal-remoterpc-connector integrates with DOMRpcRouter, but that integration needs to be redone to fix BUG-3128. That in turn breaks assumptions in blueprint.

Refine the odl:rpc-service contract to cover registration semantics with respect to routed RPCs and implement it in a way, which will not break in absence of sal-remoterpc-connector.