Fix concurrency issue in routing_instance_test

Use atomic int for notification counts. Since atomic int are not
initialized to 0, move around the calls to ClearCounters so that
we call ClearCounters after a new table is created.

Change-Id: Icf0bbd05a0115b3532320c0a43f1f4fd21f04f86
Merge "Fix concurrency issue in routing_instance_test"