RFR (XXS): 8247748: Use default alpha for G1 adaptive IHOP allocation rate calculation

[Thomas Schatzl]

Hi all,

   can I have reviews for this change that tones down the g1 adaptive 
ihop allocation rate prediction to not follow the most recent allocation 
rate that much?

Instead of 0.95, use the default 0.7.

CR:
https://bugs.openjdk.java.net/browse/JDK-8247748
Webrev:
http://cr.openjdk.java.net/~tschatzl/8247748/webrev/
Testing:
tier1-3

Thanks,
   Thomas