Disable strict mode in MySQL

Closed username-removed-423915 requested to merge disable-strict-mode-for-mysql into master

What does this MR do?

Disable strict mode in MySQL

Why was this MR needed?

Because otherwise it's breaking Rails 5. See: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12841#note_40884022

There's also a failed attempt at: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14383

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?