RFR 8178604: JVM does not allow defining boot loader modules in exploded build after module system initialization

[harold seigel]

Hi,

Please review this JDK-10 bug fix to allow defining of modules to the 
boot loader in exploded builds after module system initialization.  The 
fix uses the module lock to synchronize access to the _exploded_entries 
data structure (which is only used by exploded builds).

Note that the above capability already exists for regular builds.

Open Webrev: 
http://cr.openjdk.java.net/~hseigel/bug_8178604/webrev/index.html

JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8178604

The fix was tested with JCK tests, the JTreg hotspot, java/io, 
java/lang, java/util and other tests, the RBT tier2 -tier5 tests, the 
co-located NSK tests, and with JPRT.  The JTReg and JCK tests were run 
with an exploded build.  Also, the example program in the JBS bug was 
run by hand to verify the fix.

Thanks, Harold