On databases such as MySQL, it's possible to get into a timing comparison
error if the value of `Confirmable#confirmation_sent_at` is within a second
of `0.days.ago`. This is possible mostly in specs that test this behavior
and most likely not happening in practice. The result of this error causes
a user to be deemed active when it should be inactive. To prevent this
error, we explicitly check the configuration setting to be `0.days.ago`.

Closes gitlab-org/gitlab-ee#2362