Hostport deletion fails when VM doesn't exist anymore

Created by: arnaudsjs

The dependency manager ensures that a VM is deployed before its HostPort(s). On deletion this causes a problem since the read_resource() method of the HostPort handler, expects the VM to exist (see: https://github.com/inmanta/openstack/blob/08c4dc0be9c2149e8bd9e815780f8c26009659f8/plugins/init.py#L2138).