Provide information on MD-SAL's "Ready" status

Northbound and southbound clients need to know when MD-SAL is "ready" to be utilized.

In this case, ready means, all OOB models have been loaded, and services have been published to the OSGi container.

WE should provide some type of status identifier to help northbound / southbound clients track the "status" of the controller (specific to MD-SAL to start?)