I followed the test case from the bug description using the version of update-manager in zesty-proposed, 17.04.8, and can confirm that a new error message was displayed which suggested using 'sudo apt autoremove' to clean up old kernels.
I followed the test case from the bug description using the version of update-manager in zesty-proposed, 17.04.8, and can confirm that a new error message was displayed which suggested using 'sudo apt autoremove' to clean up old kernels.