build concurrency

[Maurizio Cimadamore]

Hi,
I realized that the concurrency factor inferred by the JDK build might 
be too high; on a 16 core machine, concurrency is set to 14 - which then 
leads to absurd load averages (50-ish) when building/running tests. High 
load when building is not a big issue, but when running test this almost 
always turns into spurious failures due to timeouts. I know I can 
override the concurrency factor with --with-jobs - but I was curious as 
to why the default parameter is set to such aggressive value?

Thanks
Maurizio