sunsetting support for Java 8

[Rick Hillegas]

My experience working on DERBY-6856 suggests that it will be very 
difficult to support building Derby with both JDK 9 and earlier versions 
of the JDK. In previous releases, we maintained some very complicated 
machinery for using old JDKs in order to build Derby jars which could 
run on both old and modern Java versions. It is hard to sustain that 
complexity given our small number of active contributors.

I propose that 10.14.1 
(https://wiki.apache.org/db-derby/DerbyTenFourteenOneRelease) be the 
last release which runs on Java 8. The 10.15.1 release would be compiled 
into Java 9 byte code and only run on that platform and later versions 
of Java. We would announce this change in the 10.14.1 release notes.

What are your thoughts? If the community seems willing, I will call a 
vote to approve this change.

Thanks,
-Rick