[11u] RFR: 8214003: Limit default test jobs based on memory size

[Severin Gehwolf]

Hi,

Please review this backport of a reliability fix for running tests.
Currently on certain machines where num_cores/2 > mem_in_gb/2 there is
a risk of tests failing due to memory issues. JTREG's -concurrency
setting will currently be num_cures/2 and the available memory for this
might not be sufficient to run the tests.

The JDK 12 patch didn't apply cleanly due to some whitespace/context
differences and a difference in argument's numbers in
RunTestsPrebuilt.gmk (due to jcov work not present in JDK 11. i.e. JDK-
8217761 and friends). The patch had to be done manually.

This patch depends on the backport for JDK-8211727 here:
http://mail.openjdk.java.net/pipermail/jdk-updates-dev/2019-August/001747.html

Bug: https://bugs.openjdk.java.net/browse/JDK-8214003
webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8214003/jdk11/01/webrev/
original changeset: http://hg.openjdk.java.net/jdk/jdk/rev/8c887dcd5d90

Testing: tier1 on Linux x86_64. Smoke tested "make run-test-prebuilt".
I didn't have access to a specific system which matches the conditions
for this bug to surface, though. Appreciate any testers.

Thoughts?

Thanks,
Severin