Code review comment for ~danielruthardt/cloud-initramfs-tools:feature/multiple-overlayroot-devices

I have removed the following part of the PR and will submit a more complete, but thus also slightly more complex, separate PR.

🚸 Improve ro detection for when both are present
Improve root file system "ro" detection for when both "ro" and "rw" are present in the kernel command line.
The above is helpful for situations when one only controls an append to the kernel command line and is not in complete control of the entire command line to be able to remove the "ro".