Description of problem:

In a scenario where the clusterNetwork is configured with a specific network range + hostprefix, once the available subnets are assigned to the maximum quantity of nodes, the host-subnets from new nodes are configured considering duplicate information where this causes timeouts and pod-to-pod communication issues in the platform. 

See the example below:

    clusterNetwork:
    - cidr: 10.xx.0.0/18
      hostPrefix: 22

A cidr /18 + hostPrefix 22 is able to assign host-subnets to 16 nodes. Once the cluster has 17 nodes, the new node is going to have a duplicate network already assigned to the nodes present in the cluster. In the following example, the cluster has 21 nodes and 5 networks are duplicate: 

$ oc get nodes -oyaml | grep k8s.ovn.org/node-subnets | awk '{print $2}' | sort
'{"default":["10.xx.0.0/22"]}'
'{"default":["10.xx.12.0/22"]}'
'{"default":["10.xx.16.0/22"]}'
'{"default":["10.xx.20.0/22"]}'
'{"default":["10.xx.24.0/22"]}'
'{"default":["10.xx.28.0/22"]}'
'{"default":["10.xx.32.0/22"]}'
'{"default":["10.xx.36.0/22"]}'
'{"default":["10.xx.40.0/22"]}'
'{"default":["10.xx.4.0/22"]}'
'{"default":["10.xx.44.0/22"]}'
'{"default":["10.xx.48.0/22"]}'
'{"default":["10.xx.48.0/22"]}' <--
'{"default":["10.xx.52.0/22"]}'
'{"default":["10.xx.56.0/22"]}' 
'{"default":["10.xx.56.0/22"]}' <--
'{"default":["10.xx.56.0/22"]}' <--
'{"default":["10.xx.56.0/22"]}' <--
'{"default":["10.xx.56.0/22"]}' <--
'{"default":["10.xx.60.0/22"]}'
'{"default":["10.xx.8.0/22"]}'

No error message is reported in the OVN-K's components. The OVN-K should not allow these network assignments. 

Version-Release number of selected component (if applicable): 4.14.37

How reproducible: Easily. 

Steps to Reproduce:

Configure a small clusternetwork and create a high quantity of nodes to cause the duplicate networks.

Actual results: No messages are reported  except the following in the northd pod: 

northd|WARN|No path for static route 10.xxx.56.0/22; next hop 10.xxx.56.2 

Expected results: It should not allow duplicate networks.