RFR 8021883 j.u.Random/RandomStream.java test needs more robust timeout duration

[Chris Hegarty]

Paul,

This looks like a nice cleanup, as well as fixing the timeout issue.

I just don't get the change in failure criteria. The old test used to 
verify that the arrays of random numbers of all generating threads were 
not equal, but now your checking the number of tasks?

-Chris.

> Hi,
>
> http://cr.openjdk.java.net/~psandoz/tl/JDK-8021883-random-stream-test/webrev/
>
> This patch updates tests for ThreadLocalRandom streams and increases the timeout duration. Although the original should be enough for most cases in certain virtualized and emulated environments it might not be. I also took the liberty of consolidating the code and sprinkling stream and CompletableFuture dust on things.
>
> Paul.
>