RFR (S): [TESTBUG] Test for JDK-8180048

[Thomas Schatzl]

Hi all,

  can I have some reviews that adds a test for JDK-8180048? That test
has not been completed in time for JDK 9, but I think it is good to
have it in JDK 10.

It tries to detect the races fixed in JDK-8180048 by parsing NMT output
before/after symbol unloading. To be sure that we exercise the buggy
code path, the test takes some time (~30s) to stress symbol unloading.

To avoid this test clogging up valuable time in lower testing tiers,
the test has been put into the "stress" test directory so that it only
executes at higher test tiers. Further I limited it to execute only
with a release build.

CR:
https://bugs.openjdk.java.net/browse/JDK-8180280
Webrev:
http://cr.openjdk.java.net/~tschatzl/8180280/webrev
Testing:
test case passing

Thanks,
  Thomas