Change clientId to random clientId

The client identifier should be unique across all clients connecting to the same server. A convenience method is provided to generate a random client id that should satisfy this criteria - generateClientId(). Returns a randomly generated client identifier based on the current user's login name and the system time. As the client identifier is used by the server to identify a client when it reconnects, the client must use the same identifier between connections if durable subscriptions are to be used.