RFR(S) 8172288: Fix error message when trying to define an existing package to a module

[harold seigel]

Hi,

Please review this small fix for JDK-8172288.  Here's a sample of the 
new message:

Package mypackage6 for module dupl.pkg.module is already in another 
module, Module_A, defined to the class loader

Adding the class loader name to the message will be done as part of 
JDK-8169559 <https://bugs.openjdk.java.net/browse/JDK-8169559>.

Open Webrev: 
http://cr.openjdk.java.net/~hseigel/bug_8172288/webrev/index.html

JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8172288

The fix was tested with the JTreg hotspot, java/io, java/lang, java/util 
and other JTReg tests, and the NSK co-located and non-colocated tests.

Thanks, Harold