Ignore the /var/lib/ureadahead/debugfs mount
Ignore the /var/lib/ureadahead/debugfs mount

We're hitting a bug where `/var/lib/ureadahead/debugfs` is being added to the mount
structure at somepoint in the boot and then being removed. This is causing

`DISK CRITICAL - /var/lib/ureadahead/debugfs/tracing is not accessible: No such file or directory`

as mountall adds everything it finds, but doesn't remove it when it goes away. We don't use the
tracing functionality and we're not in a position to test removing ureadahead so for now
we'll ignore the partition and allow the check to function as it used to.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet