RFR : 8147772, 8163104

[Seán Coffey]

Looking to backport the following two bug fixes to jdk8u-dev :

JDK-8147772 Update KerberosTicket to describe behavior if it has been 
destroyed and fix NullPointerExceptions
JDK-8163104 Unexpected NPE still possible on some Kerberos ticket calls

The changes are similar to JDK 9 expect that the @implNote and javadoc 
edits have been omitted from jdk8u for the 8147772 port.

webrev : 
http://cr.openjdk.java.net/~coffeys/webrev.8147772.8163104.jdk8u/webrev/

-- 
Regards,
Sean.