This commit deprecates `[pod_vif_nested]worker_nodes_subnet` in favor of
`[pod_vif_nested]worker_nodes_subnets` that will accept a list instead.
All the code using the deprecated options is updated to expect a list
and iterate over possible nodes subnets.
Change-Id: I7671fb06863d58b58905bec43555d8f21626f640
b3814a33d6