Unit test for SEBA-646 (cordmcast should listen to multicast events from the new multicast store)

Unit test for cordmcast -

Cordmcast should listen to multicast events from the new multicast store.

Below are the different test case scenarios added:

1) Adding sink in the group.

2) Adding another output port to the existing sink.

3) Removing sink from the group.

4) Testing if the device is unknown olt device.

5) Testing Route Added Mcast event.

6) Testing Route Removed Mcast event.

7) Testing Source Added Mcast event.

8) Testing Source Removed Mcast event.

9) Removing last sink from the group.