Basic networks Scenario Test Enhancements

Add test to update router admin_state_up attribute of the router
-Update admin_state_up attribute of router to False and check public
 connectivity
-Update admin_state_up attribute of router back to True and check public
 connectivity again

Change-Id: I3fd56c44411ff6919e15dd1033f6c13e58271f4b
Merge "Basic networks Scenario Test Enhancements"