RFR (XS): 8196550: [Testbug] runtime/appcds/MultiReleaseJars.java fails on JDK 11

[David Holmes]

webrev: http://cr.openjdk.java.net/~dholmes/8196550/webrev/
bug: https://bugs.openjdk.java.net/browse/JDK-8196550

The test creates a MR jar utilising the "current version" of the JDK, 
which is passed to "javac --release" - but the support for --release 11 
is not yet available in javac. Simple fix is to temporarily hard-wire 
version 10 as the "current" release.

-    static final int MAJOR_VERSION = Runtime.version().major();
-    static final String MAJOR_VERSION_STRING = 
String.valueOf(Runtime.version().major());
+    static final int MAJOR_VERSION = 10; // Runtime.version().major();
+    static final String MAJOR_VERSION_STRING = 
String.valueOf(MAJOR_VERSION);

This will be pushed to jdk/jdk ready for the version bump.

Alternatively we can problem-list the test until javac is ready - but I 
thought it better to actually keep testing AppCDS.

Thanks,
David