Cluster support

[simon622]

Should have the ability to synchronise connections across VMs. The state that would need to be synchronised is as follows;

Client Id Outbound messages queue Subscriptions Will data Last seen Session expiry interval Max packet size Retain behaviour (from CONNECT)

The cluster service gets notified upon new client side connection of the connecting clientId. If cleanStart = false then the state from existing session in the cluster should be synchronised to local connected gateway. If cleanStart is true the cluster still needs to be notified to clean up state held elsewhere.

If a connection is ACTIVE or SLEEPING on another node in the cluster, it should be terminated and removed after synchronisation occurs.