RFR(S): 8241033: Create test library utility for getting JFR streaming repository

[Erik Gahlin]

Looks good! This will make it easier to debug failures, 

Erik

> On 17 Mar 2020, at 00:50, mikhailo.seledtsov at oracle.com wrote:
> 
> Please review this change that introduces a test library utility for obtaining a JFR streaming repository.
> Several tests use this functionality, and each implement their own methods. This change unifies the functionality, and also
> improves it including added diagnostics.
> 
>     JBS: https://bugs.openjdk.java.net/browse/JDK-8241033
>     Webrev: http://cr.openjdk.java.net/~mseledtsov/8241033.02/
>     Testing:
>        Ran open/test/jdk/jdk/jfr/api/consumer/streaming/
>            PASS
> 
> 
> Thank you,
> Misha
>