RFR 8185717: Make ModuleEntry->module() return an oop not a jobject

[harold seigel]

Hi,

Please review this JDK-10 change to have ModuleEntry::module() return an 
oop instead of a jobject.

Open Webrev: 
http://cr.openjdk.java.net/~hseigel/bug_8185717/webrev/index.html

JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8185717

The fix was tested with the JCK Lang and VM tests, the JTreg hotspot, 
java/io, java/lang, java/util and other tests, the co-located NSK tests, 
JPRT, and with the RBT tier2 - tier5 tests on Linux x64.

Thanks, Harold