[Merge] ~danielruthardt/cloud-initramfs-tools:feature/multiple-overlayroot-devices into cloud-initramfs-tools:master

[Daniel Ruthardt]

The separate PR for the improved/fixed ro detection can now be found here: https://code.launchpad.net/~danielruthardt/cloud-initramfs-tools/+git/cloud-initramfs-tools/+merge/460784
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https://code.launchpad.net/~danielruthardt/cloud-initramfs-tools/+git/cloud-initramfs-tools/+merge/460349
Your team Ubuntu Sponsors is requested to review the proposed merge of ~danielruthardt/cloud-initramfs-tools:feature/multiple-overlayroot-devices into cloud-initramfs-tools:master.