I followed the test case from the bug description using the version of update-manager in zesty-proposed, 16.04.10, 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, 16.04.10, and can confirm that a new error message was displayed which suggested using 'sudo apt autoremove' to clean up old kernels.