Update metadata.php

Without this unable to access AD info. Also allows SSO.

lib/plugins/authad/conf/metadata.php

@@ -4,11 +4,11 @@ $meta['account_suffix']     = array('string');
 $meta['base_dn']            = array('string');
 $meta['domain_controllers'] = array('string');
 $meta['sso']                = array('onoff');
-$meta['ad_username']        = array('string');
-$meta['ad_password']        = array('password');
+$meta['admin_username']        = array('string');
+$meta['admin_password']        = array('password');
 $meta['real_primarygroup']  = array('onoff');
 $meta['use_ssl']            = array('onoff');
 $meta['use_tls']            = array('onoff');
 $meta['debug']              = array('onoff');
 $meta['expirywarn']         = array('numeric', '_min'=>0);
-$meta['additional']         = array('string');
\ No newline at end of file
+$meta['additional']         = array('string');