Structured concurrency for Completable/Listenable futures

[elizarov]

kotlinx-coroutines-jdk8and kotlinx-coroutines-guava integration modules' future { ... } builders do not honor structured concurrency in the same way as all other builders -- a failure inside the child (builder) code did not cancel the parent coroutine. This change is to address this discrepancy and to bring them inline with all the the other builders, both core ones (launch, async, produce, etc) and from other integration modules (rxSingle, publish, etc).

Note that this change does not affect non-structured (typical) usage like GlobalScope.future { ... }.

Please note, that there is an open design issue (#763) regarding async { ... } and this change "deepends" this problem by bringing future { ... } inline with this structured concurrency behaviour. However, this is not a major issue for future { ... } since it is integration vehicle that is typically used to adapt suspending function to the Java code that expects a future result like this:

suspend fun doSomething(): T { .... } // Kotlin fun

fun doSomethingAsync(): CompletableFuture<T> = GlobalScope.future { // Java fun
     doSomething()
}