RFR (S): JDK-8228504: Rename max_rs_length to young_rs_length

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that fixes the identifier
"max_rs_length" across G1 code?

The problem with it is that it is no maximum of a single remembered set
length, but a sum, and to clarify that it is supposed to be the sum of
young gen remembered set lengths, this change calls it
"young_rs_length".

With that change the issue in JDK-8228505, that we add old remembered
set lengths to it during mixed gc, immediately stands out. Fixed in
that change.

Based on JDK-8228503.

CR:
https://bugs.openjdk.java.net/browse/JDK-8228504
Webrev:
http://cr.openjdk.java.net/~tschatzl/8228504/webrev/
Testing:
hs-tier1-3

Thanks,
  Thomas