Provide a default ldap.guidAttribute for Open LDAP

This adds a new default value for ldap.guidAttribute for Open LDAP, which should address https://github.com/pwm-project/pwm/issues/188 - at least for new new installations.  For existing installations, I've included a config fragment which seemed to fix the bug for me.

server/src/main/resources/password/pwm/config/PwmSetting.xml

@@ -576,6 +576,9 @@
         <default template="ORACLE_DS">
             <value><![CDATA[pwmGUID]]></value>
         </default>
+        <default template="OPEN_LDAP">
+            <value><![CDATA[entryuuid]]></value>
+        </default>
     </setting>
     <setting hidden="false" key="ldap.namingAttribute" level="1" required="true">
         <ldapPermission actor="proxy" access="read"/>