[OpenJDK 2D-Dev] RFR 8140314: Verify IIOMetadataFormat class on loading

[Phil Race]

https://bugs.openjdk.java.net/browse/JDK-8140314
http://cr.openjdk.java.net/~prr/8140314.1/

This code was refactored a fair amount in preparation for jigsaw and was 
failing
at one point when Class.forName(Module, String) did not work for the 
un-named module.

Now the residual issue is that we should verify it is actually the right 
type before
we return and get a CCE in the calling code.

I ran all imageio regression and tests and there were no (new) failures.

-phil.