Set isReceivingInitialDiskSnapshot to false on non-replica->active transition

Currently we set this flag to false when transitioning from replica to active. The idea behind this is that we may have not yet received a full snapshot but have been promoted so we now need to stream what data we have to other nodes. It is valid to transition from pending to active also, and in general we should never make any assumptions about what state transitions are possible, so we should set this flag to false when transitioning from any state to active.

If we do not, then we risk being unable to replicate data from 1 node to another in the event of a hard failover.