use (new) node3_hosts group for check that only runs on node3

manifests/sitemonitornaemon.pp

@@ -108,7 +108,7 @@ class sunetdrive::sitemonitornaemon() {
     contact_groups => ['alerts']
   }
   nagioscfg::service {'check_nextcloud_mounts':
-    hostgroup_name => ['sunetdrive::application','sunetdrive::multinode'],
+    hostgroup_name => ['node3_hosts','sunetdrive::multinode'],
     check_command  => 'check_nrpe_1arg!check_nextcloud_mounts',
     description    => 'S3 buckets with multiple Nextcloud mounts',
     contact_groups => ['alerts']