There are cases when nailgun can send us data where there are nodes
included into list of added nodes and deleted ones. As a result, puppet
manifests failed with resource ensurance for present and absent hosts.
To avoid this situation, subtract added nodes from deleted prior to
actually deleting them from hosts.
Change-Id: I515f7fae4bbe67123d70572a4f861e879ec580f6
Closes-Bug: #1679522