DERBY-6613: StatementPoolingTest fails on JDK 9

Check for JDBC 4.2 support in the JVM (that is, Java 8 or higher)
instead of checking for Java 8.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1602087 13f79535-47bb-0310-9956-ffa450edef68