RFR (S) CR 8023638: Add the regression test for 8006997

[Aleksey Shipilev]

Hi,

The latest bug scrub identified one of the issues lacking the regression
test, where it does make sense to create one.

Background: -XX:ContendedPaddingWidth=# is range-checked on VM side to
be in [0; 8192], plus being the multiple of 8. The test checks multiple
values around the failure point.

Here's the webrev:
  http://cr.openjdk.java.net/~shade/8023638/webrev.00/

Testing:
  - this test is trivial, and excersises the common code path in VM,
hence only Linux x86_64/release was tested.

Please review!

Thanks,
-Aleksey.