RFR JDK-8179614: Test for jarsigner on verifying jars that are signed and timestamped by other JDK releases

[sha.jiang at oracle.com]

Hi,
Please review this manual test for checking if a jar, which is signed 
and timestamped by a JDK build, could be verified by other JDK builds.
It also can be used to check if the default timestamp digest algorithm 
on signing is SHA-256.
For more details, please look through the test summary.

Issue: https://bugs.openjdk.java.net/browse/JDK-8179614
Webrev: http://cr.openjdk.java.net/~jjiang/8179614/webrev.00/

Best regards,
John Jiang