RFR (S): CR 8006697: ContendedPaddingWidth should be range-checked

[Aleksey Shipilev]

Hi,

Long-lasting fix for this CR is available here:
  http://cr.openjdk.java.net/~shade/8006997/webrev.03/

We need to test for the sensible padding sizes, as well as the
alignment. Hence, these two checks during startup. I had selected [0;
8192] bytes as the sensible range for padding, please speak up if you
think this is wrong.

Testing:
  - full JPRT cycle
  - adhoc cmdline testing with Linux x86_64/fastdebug
    (the issue is trivial enough so I haven't built the jtreg test)

-Aleksey.