RFR 8206424: Use locking for cleaning ProtectionDomainTable

[Patricio Chilano]

Hi all,
Could you review this fix that moves the cleanup of dead entries in the 
protection domain table from the VMThread to the ServiceThread.
The goal is the same as JDK-8206423. The task of cleaning up dead 
entries in the protection domain table was moved to the ServiceThread.
The fix was tested with Mach5 on tiers 1, 2, 3 on all platforms. A new 
test (test/hotspot/jtreg/runtime/appcds/CleanProtectionDomain.java) was 
added to test the creation and removal of entries in the Protection 
Domain table.
Bug URL: https://bugs.openjdk.java.net/browse/JDK-820642 
<https://bugs.openjdk.java.net/browse/JDK-8206423>4
Webrev 
URL: http://cr.openjdk.java.net/~pchilanomate/8206424.01/webrev/index.html
Thanks,
Patricio