Subnet marked as available even when router interface can't be created

[mandre]

Create a subnet with:

---
apiVersion: openstack.k-orc.cloud/v1alpha1
kind: Subnet
metadata:
  name: subnet
spec:
  cloudCredentialsRef:
    cloudName: openstack
    secretName: openstack-clouds
  managementPolicy: managed
  networkRef: existing-network
  resource:
    ipVersion: 4
    cidr: 192.168.0.0/24
    routerRef: non-existing-router

ORC will happily create the subnet and mark it as available, even though the router does not exist, and the router interface never moves to available.