RFR (XS): 8179677: Rename G1RemSet::conc_refine_cards() to something more appropriate

[Thomas Schatzl]

Hi all,

  during the reviews of the recent patch queue for changing remembered
set refinement/scanning one reviewer asked for renaming of
the G1RemSet::conc_refine_cards() method and related members because
the name indicates that this value counts the number of concurrently
refined cards, while in reality it counts the number of ever refined
cards (since day one).

This change fixes this by renaming the member to "num_refined_cards".

CR:
https://bugs.openjdk.java.net/browse/JDK-8179677
Webrev:
http://cr.openjdk.java.net/~tschatzl/8179677/webrev/
Testing:
local compilation

It depends on the patches presented in the email thread starting at htt
p://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2017-
April/019653.html .

Thanks,
  Thomas