RFR: 8004488 wrong permissions checked in krb5

[Seán Coffey]

I'm looking to backport this fix to JDK 7u code line. The fix applies 
pretty much as is with the JDK 8 fix with the exception of not having to 
deal with a ServiceCreds tgt variable (Krb5Util.java) which was only 
introduced in JDK 8 for : 6355584: Introduce constrained Kerberos delegation

bug : https://bugs.openjdk.java.net/browse/JDK-8004488
webrev : http://cr.openjdk.java.net/~coffeys/webrev.8004488.7u/webrev/

Tests are green.

Regards,
Sean.