RFR (XXS): 8143220: Fix documentation of InitiatingHeapOccupancyPercent

[Thomas Schatzl]

Hi all,

  can I have reviews for this change to the documentation of the
 InitiatingHeapOccupancyPercent global? I think due to recent changes
to the behavior it is warranted that the (internal) documentation
reflects it.

Other suggestions for the text welcome.

CR:
https://bugs.openjdk.java.net/browse/JDK-8143220
Webrev:
http://cr.openjdk.java.net/~tschatzl/8143220/webrev/
Testing:
local compilation

Thanks,
  Thomas