RFR 8071313: krb5.conf not read if SCDynamicStore krb5 config is empty

[Wang Weijun]

Hi All

Please review the fix at

  http://cr.openjdk.java.net/~weijun/8071313/webrev.00

On a Mac OS X, when Open Directory is installed but disabled, Java should be able to use other Kerberos settings.

Noreg-hard but I added a comment [1] to describe how to test the change.

Thanks
Max

[1] https://bugs.openjdk.java.net/browse/JDK-8071313