RFR[12] JDK-8209546: Make sun/security/tools/keytool/autotest.sh to support macosx

[sha.jiang at oracle.com]

Hi,
JDK-8164639 removed NSS libs from repo, so 
sun/security/tools/keytool/autotest.sh has to download NSS libs from 
artifactory on macosx.
This patch also refactors this shell test to a Java test.

Webrev: http://cr.openjdk.java.net/~jjiang/8209546/webrev.00/
Issue: https://bugs.openjdk.java.net/browse/JDK-8209546

Best regards,
John Jiang