AB Testing: RemoteCacheSignal; sometimes the timer's callback was called before the timer completed initialization

Description

The System.Threading.Timer in RemoteCacheSignal was initialized with dueTime set to 0 in RemoteCacheSignal.Monitor() method. This sometimes led to the Timer's callback being called immediately when the Timer object had not finished initialization and some of its properties were still null. However, the callback tried to access the Timer with Change() method and this led to a null reference exception and sometimes crashed the web server.