RFR (S): 8202021: Improve variable naming in ReferenceProcessor

[Thomas Schatzl]

Hi all,

  can I have reviews for this cleanup change that improves variable
naming in ReferenceProcessor code.

The main change is about renaming some member variables from something
really confusing to me to something useful (to me again :)) in the
DiscoveredListIterator class.

The other change is related to changing ReferenceProcessor::num_q to
num_queues, i.e. spelling out what the "q" is supposed to mean.

That imho improves readability quite a bit.

CR:
https://bugs.openjdk.java.net/browse/JDK-8202021
Webrev:
http://cr.openjdk.java.net/~tschatzl/8202021/webrev/
Testing:
local compilation, hs-tier1-4 with 8202017

based on JDK-8202018, but I do not think there is overlap.

Thanks,
  Thomas