Add refreshKrb5Config=true option to Kerberos JAAS configuration

Allows system properties to be used to specify KDC/Realm name and can be changed.

Alternately, the WinrmClient could be changed to support specifying a custom configuration class for specific needs.  This change seemed simplest. I don't think it would have much effect for people who don't need it but it allows some people to use the java System properties to specify KDC/realm, and then later modify those system properties.