Database SSL support for backup script.

What does this MR do?

It allows the backup script not to fail for creating DB backups in the case a MySQL/PostgreSQL server using SSL connection is used to host the GitLab database.

Are there points in the code the reviewer needs to double check?

Not realy, tested against a SSL-enabled and non-SSL MySQL server and a PostgreSQL one.

Why was this MR needed?

To fix https://gitlab.com/gitlab-org/gitlab-ce/issues/1440

Does this MR meet the acceptance criteria?

• Changelog entry added
• [n/a] Documentation created/updated
• [n/a] API support added
• Tests
  • [n/a] Added for this feature/bug
  • All builds are passing
• [n/a] Conform by the merge request performance guides
• Conform by the style guides
• [n/a] Branch has no merge conflicts with master (if it does - rebase it please)
• [ x] Squashed related commits together

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/1440

Notes

• MySQL options are those available with currently used mysql2 adapter gem version.
• PGSQL options are passed as connection parameters to libpq.