Check if commandline policy needs to be added

if there are further arguments to kernel.efi, and thus /etc/kernel/cmdline exists on the root partition, commandline policy should be added.

See https://github.com/canonical/nullboot/issues/53

Start by reviewing how kernel.efi arguments and commandline policy are handled, then read /etc/kernel/cmdline and the referenced nullboot issue 53 for the expected behavior. Done means confirming whether extra kernel arguments exist and adding the corresponding commandline policy when they do.

Written by the indexing model from the issue text.