RFR (S): 8200426: Make G1 code use _g1h members

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that tries to make the use of
locally cached members of G1CollectedHeap* uniform by actually using it
and renaming the members uniformly to "g1h".

This change has been suggested in a recent review.

There has not actually been a lot to change.

CR:
https://bugs.openjdk.java.net/browse/JDK-8200426
Webrev:
http://cr.openjdk.java.net/~tschatzl/8200426/webrev
Testing:
local compilation

Thanks,
  Thomas