[9] RFR: 8168882: keytool doesn't print certificate info if disabled algorithm was used for signing a jar

[Artem Smotrakov]

Hello,

Please review this small update for keytool.

"keytool -printcert -jarfile" doesn't work with jars which were signed 
with algorithms listed in "jdk.jar.disabledAlgorithms" security property.

The patch below resets "jdk.jar.disabledAlgorithms" security property 
before reading a jar file, and prints a warning.

I also re-wrote readjar.sh test, and added SecurityTools class with a 
couple of re-usable methods for jarsigner and keytool (those methods are 
based on methods from TimestampCheck.java).

Bug: https://bugs.openjdk.java.net/browse/JDK-8168882
Webrev: http://cr.openjdk.java.net/~asmotrak/8168882/webrev.00/

Artem