Add support for slash_16 networks

Hello,

EnOSlib allows to allocate slash_16 networks (as 64 slash_22 networks), but this is not supported by kube5k because it expects a single slash_22 network from EnOSlib.

According to the code of EnOSlib, there is no way to differentiate between them beside checking the length of the return value. So do that, and if a slash_16 is detected, return the /16 netmask of the first /22 network returned by EnOSlib.

I used this successfully on G5k for K8S clusters with more than 4 nodes (9 nodes) with otherwise default configuration, using flannel for the networking, for both the pod and service networks.