RFR (S) 8164207: Checking missing load-acquire in relation to _pd_set in dictionary.cpp

[coleen.phillimore at oracle.com]

Summary: Use load_acquire for accessing DictionaryEntry::_pd_set since 
it's accessed outside the SystemDictionary_lock

Ran parallel class loading tests that we have as well as tier1 tests.   
See bug for details.

open webrev at http://cr.openjdk.java.net/~coleenp/8164207.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8164207

Thanks,
Coleen