RFR: JDK-8211727: Adjust default concurrency settings for running tests on Sparc

[Erik Joelsson]

This patch changes the formula for default test concurrency in 
RunTest.gmk. The current formula is:

min(cpus/2, 12)

This seems to work well enough on the x64 machines we currently run our 
tests on, but less so for Sparc. I have now run rather extensive testing 
in our lab and have come up with a new formula that provides much better 
test reliability while preserving as much test throughput as possible. 
The new formula is cpus/4 for sparcs with up to 16 cpus and cpus/5 for 
larger machines. For non Sparc it's still cpus/2 and I've removed the 
cap for all.

In addition to this, since Sparc generally have lower per thread 
performance, at least when running JDK tests, I have bumped the default 
timeout factor from 4 to 8 for Sparc.

With these defaults, we were able to remove a lot of special cases for 
Sparc in other parts of our configurations and I was able to get clean 
runs of all the lower tiers of testing, on each of our machine classes 
in the lab.

In addition to this, the test 
compiler/jsr292/ContinuousCallSiteTargetChange.java, which had its 
timeout increased in JDK-8212028, no longer needs an increased timeout 
with the new defaults.

Bug: https://bugs.openjdk.java.net/browse/JDK-8211727

Webrev: http://cr.openjdk.java.net/~erikj/8211727/webrev.01/

/Erik