RFR (S): 8252035: G1: Clean up G1CollectedHeap::*reserved* methods

[Thomas Schatzl]

Hi all,

  can I have reviews for this change the cleans up the G1CollectedHeap::*reserved* methods?

Includes some renaming and removal of half of these methods after refactoring the code a little to make them obsolete.

Based on 8252034 also out for review.

CR:
https://bugs.openjdk.java.net/browse/JDK-8252035
Webrev:
http://cr.openjdk.java.net/~tschatzl/8252035/webrev
Testing:
tier1

Thanks,
  Thomas