Proxy controller services in DOMMountPointServiceImpl

Proxy controller services in DOMMountPointServiceImpl

When we are proxying a DOMMountPoint, we also need to take care
of bridging legacy interfaces on top of MD-SAL interfaces.

This patch refactors DOM{Notification,Rpc}Router to factor out
DOM{Notification,Rpc}Service adapters and creates DOMActionService
adapter. These are then used in DOMMountPointAdapter, which in
turn is used by DOMMountPointServiceImpl.

This deals with the case when an MD-SAL-registered mount point
is accessed via Controller APIs.

JIRA: CONTROLLER-1869
Change-Id: Ide4c636afdbd13e233880ab616aec52e46ea115f
Signed-off-by: Jakub Morvay <jmorvay@frinx.io>
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>