VLAN, subnet, storage5k and disk resources have a field
network_address whose value is "" (blank) in OAR database, and they
are the sole resources with blank network_address.

We want the method "status" to display only nodes status and not VLAN,
subnet, storage5k, and especially not disk status.

In this commit, I remove these resources from the "status" method, by
removing resources with blank network_address.