Modify response to indicate to clients that the host is shutting down

- This enables LongPolling to reconnect like other transports during shutdown
- No longer reconnect after connection timeout with the .NET client

#2188
#2323
Change "timedOut" to "shouldReconnect" in .NET client's ProcessResponse

#2188
#2323
Added test to verify reconnect fires after host shutdown with LP

#2188
Updated JS client to trigger reconnect event after host shutdown

#2188