RFR: JDK-8214003: Limit default test jobs based on memory size

[Tim Bell]

Erik:

> On machines with a small amount of memory compared to number of cpus, we
> see test failures, and sometimes very long test run times (due to
> swapping). Because of this we need to limit the default TEST_JOBS based
> on memory size, just like we do for build JOBS in configure.
>
> This patch adds a limit at "memory in GB" / 2, which seems to alleviate
> the problem for our particular hosts.
>
> Webrev: http://cr.openjdk.java.net/~erikj/8214003/webrev.01/
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8214003


Looks good.  Thanks for doing this - we can still get some useful 
testing out of legacy hardware.

Tim