singleuser.cloudMetadata.blockWithIptables to fail with better error messages

[consideRatio]

singleuser.cloudMetadata.blockWithIptables works by adding an init container to block access to the cloud metadata server.

While this hasn't happened often to my knowledge, in #3355 we had a k8s cluster setup in a way that it apparently did.

Looking back, maybe the error was that the kernel actually needed to be updated?

kubectl logs jupyter-root -n jhub -c block-cloud-metadata

modprobe: can't change directory to '/lib/modules': No such file or directory
modprobe: can't change directory to '/lib/modules': No such file or directory
iptables v1.8.9 (legacy): can't initialize iptables table `filter': Table does not exist (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded.

[manics]

Iptables was added to the Linux kernel in v3.13 https://en.wikipedia.org/wiki/Iptables so it's unlikely to be out of date!

modprobe: can't change directory to '/lib/modules': No such file or directory
This sounds like the problem, the standard kernel modules directory either isn't accessible, or is in a non-standard location.