Initial RFR: 8187302: [Nestmates] Prepare for classfile version 54 and javac "release" update

[David Holmes]

webrev: http://cr.openjdk.java.net/~dholmes/8187302/webrev/

(please ignore the two hotspot test changes)

This changes prepares for switching to release 11 and classfile version 
54 so that I can put classfile version checks where needed, and compile 
tests the right way, where needed.

Initially the default remains release 10 and v53, but --release 11 can 
be used to explicitly use v54.

I think I have found everything that needs updating to allow use of 
release 11 and v54 classfiles.

Testing so far is minimal: javac Foo.java -> v53
                            javac --release 11 Foo.java -> v54

langtools/tools/javac testing also conducted.

Thanks,
David