RFR 8075618: Create tests to check jarsigner work with multi-version jar

[Amanda Jiang]

Hi All,

Please help to review following changeset, which tests that jarsigner 
tool works with multi-release JAR files.

Webrev: http://cr.openjdk.java.net/~amjiang/8075618/webrev.01/
Bug: https://bugs.openjdk.java.net/browse/JDK-8075618


Thanks,
Amanda