Minor client changes.

1) Modified RxClientImpl.connect() to do a take(1) on the underlying source so that in no case it will emit two onNext().
2) Modified RequestProcessingOperator to use SubscriptionList instead of CompositeSubscription. Instead of creating a new subscription on every onNext(), it is done once and used by the subscriber.
3) Provided an override to remove all connection pooling for a client.