Default value not used in RPC

This bug was seen while fixing CONTROLLER-1420. I have created a new leaf in an RPC message, and provided a default value for it.

leaf count

{ type uint16; default 0; description "Number of cars to create. Zero implies unlimited cars; use stop-stress-test rpc to stop the test."; }

During tests, if the RPC does not contain the 'count', then getCount() returns null. I expect it to return 0. I had to add the value in my implementation. This is fragile, as the code has to keep track of the default value in yang model.