Make available a System Property to change Context.REFERRAL to IGNORE

By default we use FOLLOW
https://github.com/jenkinsci/active-directory-plugin/blob/d6bb427d070f35acf376f73de041d02df3be2996/src/main/java/hudson/plugins/active_directory/ActiveDirectorySecurityRealm.java#L517

http://docs.oracle.com/javase/jndi/tutorial/ldap/referral/jndi.html

This will be done through the Java Argument -Dhudson.plugins.active_directory.referral.ignore=true in case you want to set-up