RFR[13] JDK-8220410: sun/security/tools/jarsigner/warnings/NoTimestampTest.java failed with missing expected output

[sha.jiang at oracle.com]

Hi,
This fix just makes sure that specified timezone is not null, and the 
jar verifying and date formatting use the same different timezone.

Webrev: http://cr.openjdk.java.net/~jjiang/8220410/webrev.00/
Issue: https://bugs.openjdk.java.net/browse/JDK-8220410

Best regards,
John Jiang