Review request: 8157068 ExceptionInInitializerError if images build patched to use exploded version of java.lang.module.SystemModules

[Mandy Chung]

Webrev at:
  http://cr.openjdk.java.net/~mchung/jdk9/webrevs/8157068/webrev.00/index.html

This is to allow to patch java.base with an exploded image for JDK development purpose like this:
$ images/jdk/bin/java -Xpatch:java.base=jdk/modules/java.base -version

jdk.internal.module.SystemModules class is generated at link time to allow fast reconstitution of ModuleDescriptor.  If an image is patched with java.base of an exploded image, it will fall back to read and parse module-info.class from the jimage.  Hashes of tied modules are recorded in jdk.internal.module.SystemModules class in the fast path.  If patched, this fix will use the hashes recorded in the Hashes attribute for integrity check (that already validated at link time).

Mandy