Review Request: 8173381: osName/osArch/osVersion is missing in ModuleDescriptor created by SystemModules

[Mandy Chung]

The ModuleTarget attribute is added to java.base and other JDK modules when JMOD file is created but it gets dropped when the system modules plugin reconstitutes the ModuleDescriptor for fast loading.  The fix is straight-forward to add osName/osArch/osVersion if present.

Webrev at:
   http://cr.openjdk.java.net/~mchung/jdk9/webrevs/8173381/webrev.00/

thanks
Mandy