k8s: Minor adjustment to make 'configfs' kernel module optional

[rodnymolina]

I'm simply moving the modprobe instruction within an 'if' clause to prevent bash's errexit from bailing out. I verified that it works as expected with a fictitious module not present in my k8s node.

[rodnymolina]

Based on my tests, there's no need to touch the configfs entry in the 50-sysbox-mod.conf file, especially since we need it there in scenarios where configfs is present. The problem is not reproduced with my changes.