XD-1975 Fixing Exception when twitter sources undeployed

- not throwing IllegalStateException when channel adapter is stopped

- adding CountDownLatch in doStop to avoid "Dispatcher has no subscribers" message

- adding property for phase with max int value to twittersearch
I'm not keen on a `final` latch; although it will solve this particular case (destroying a module), it will cause issues if/when we implement clustering with single source instances where the ZK admin will start/stop sources multiple times as needed (to keep a single instance running). Plus, @markfisher 's suggestion of using `stop(Runnable)` is probably better than holding up the module.stop(), with a thread calling the `Runnable` when we really stopped. But, of course, that is non-trivial too, because the run() method may never call the callback, so we'd need another thread.