[9] Review Request for 8051636: DataTransferer optional dependency on RMI

[Semyon Sadetsky]

Hello,
Please review fix for JDK9-JIGSAW:

bug: https://bugs.openjdk.java.net/browse/JDK-8051636
webrev: http://cr.openjdk.java.net/~ssadetsky/8051636/webrev.00/

I have found only one run-time dependency on java.rmi module in 
sun.datatransfer.DataFlavorUtil.RMI class.
Now it checks module read access using a new ensureReadable() method 
before the rmi classes invocations.

--Semyon