RFR: 8233712: Limit default tests jobs based on ulimit -u setting

[Severin Gehwolf]

Hi,

Could I please get a review of this change for running tests on big
Aarch64 boxes? Currently, only memory and number of cores are taken
into account for the -concurrency setting of jtreg. After this patch
ulimit -u settings are taken into account as well on big Aarch64 boxes
with > 16 cores, yet low ulimit -u setting (<= 4096). This is to avoid
running into the max allowed threads limit causing random test
failures.

Thoughts?

Bug: https://bugs.openjdk.java.net/browse/JDK-8233712
webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8233712/01/webrev/

Testing: Ran tier1 tests on a large Aarch64 box and low ulimit -u
value. Tests run stable. Did the same for a user with high ulimit -u
value, which resulted in concurrency setting as before this patch.

Thanks,
Severin