Upgrade RxJava2 to 2.1.14, Upgrade AssertJ to 2.9.1

[bednar]

This Pull request also cover the RxJava2 API changes between 2.0.0 and 2.1.14

• 2.0.6: introduces specific exception wrappers to help distinguish and track down what was happening the time of the error = exceptions are wrapped in UndeliverableException - additional info
• 2.0.7: a non-positive Subscription.request() will not stop the current stream but signal an error via RxJavaPlugins.onError - additional info

Hi @JakeWharton, it is correct change for you?

[jabson009]

Good one

[JakeWharton]

Thanks, I landed a derivative of this change in #3636 which also removes the runtime backpressure support and completely removes the associated test cases.