test: Format test-only's kernel_version to avoid mistakes
test: Format test-only's kernel_version to avoid mistakes

I often try to start test-only builds with e.g.:

    test-only --kernel_version=4.19 --focus="..."

That fails because our tests expect "419". We can extend the Python
script used to parse argument to recognize that and update
kernel_version to the expected format.

Signed-off-by: Paul Chaignon <a027184a55211cd23e3f3094f1fdc728df5e0500@cilium.io>

tklauser/cilium,cilium/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,cilium/cilium,tklauser/cilium,tgraf/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,tgraf/cilium