RFR(S): 8152101: Move G1 concurrent refinement adjustment code out of G1CollectorPolicy

[Mikael Gerdin]

Hi all,

Here's yet another small G1CollectorPolicy cleanup patch.
This time I want to move adjust_concurrent_refinement out of the policy 
into the ConcurrentG1Refine class.
The method almost exclusively operates on the ConcurrentG1Refine so in 
my mind this makes perfect sense.

Bug: https://bugs.openjdk.java.net/browse/JDK-8152101
Webrev: http://cr.openjdk.java.net/~mgerdin/8152101/webrev.0/
Testing: JPRT, RBT GC testing, Perf testing in aggregate with the 
previous changes showed significant changes.

/Mikael