Fix sub-second timing comparison error for Devise confirmation period
Fix sub-second timing comparison error for Devise confirmation period

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

stoplightio/gitlabhq,stoplightio/gitlabhq,t-zuehlsdorff/gitlabhq,t-zuehlsdorff/gitlabhq,dplarson/gitlabhq,axilleas/gitlabhq,mmkassem/gitlabhq,dplarson/gitlabhq,axilleas/gitlabhq,t-zuehlsdorff/gitlabhq,axilleas/gitlabhq,axilleas/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,dplarson/gitlabhq,stoplightio/gitlabhq,stoplightio/gitlabhq,jirutka/gitlabhq,dplarson/gitlabhq,t-zuehlsdorff/gitlabhq,iiet/iiet-git,jirutka/gitlabhq,dreampet/gitlab,iiet/iiet-git,iiet/iiet-git,mmkassem/gitlabhq,jirutka/gitlabhq,dreampet/gitlab,jirutka/gitlabhq,mmkassem/gitlabhq,dreampet/gitlab,dreampet/gitlab