RFR (S) 8224151: Test vmTestbase/nsk/sysdict/vm/stress/chain/chain007/chain007.java might hang with release binaries

[coleen.phillimore at oracle.com]

Summary: Fix deadlock on ClassLoaderDataGraph_lock and g1 
clear_claimed_marks.

Thank you to Stefan for finding the deadlock and Thomas for suggestions 
on the fix, plus text for comments.

Tested with this test 100s of times, tier1-3 and tier6 almost complete.

open webrev at http://cr.openjdk.java.net/~coleenp/2019/8224151.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8224151

Thanks,
Coleen