DEV: Better error handling for destroy:users task (PR #9939)

@oblakeerickson came up with this solution while helping me debug an issue with the destroy:users task. The task would abort if a single user exceeded the limits set in the delete_all_posts_max and delete_user_max_post_age site settings.

This change will prevent the rake task from aborting when hitting the InvalidAccess error and instead output the username and error message for any users that could not be deleted.