Review Request JDK-8177844: Ensure non-upgradeable modules cannot be upgraded even with --patch-module

[Mandy Chung]

http://cr.openjdk.java.net/~mchung/jdk9/webrevs/8177844/webrev.01/

This fixes -—patch-module to do hash checking on the module being patched
so that it will ensure that a non-upgradeable module remains not upgradeable.

As Graal has been using —-patch-module option to disable the hash checking
to load a different version of jdk.internal.vm.compiler, it needs a 
mechanism to load Graal, as tracked by JDK-8177845.

Mandy