RFR: 8157605 Can't set both CONCURRENCY and EXTRA_JTREG_OPTIONS when running tests

[Tim Bell]

Staffan:

> This does not work:
>
> $ cd test
> $ make jtreg_tests CONCURRENCY=10 EXTRA_JTREG_OPTIONS=-k:\!headful
>
> I can specify either CONCURRENCY or EXTRA_JTREG_OPTIONS, but not both.
>
> Please review the fix below:
>
> bug: https://bugs.openjdk.java.net/browse/JDK-8157605 <https://bugs.openjdk.java.net/browse/JDK-8157605>
> webrev: http://cr.openjdk.java.net/~sla/8157605/webrev.00/ <http://cr.openjdk.java.net/~sla/8157605/webrev.00/>

Looks good to me.

Tim