Email Config: Fixes known SMTP TLS issue and allows new/missing attribute tls for the smtp settings
As indicated in gitlabhq issue #5636 (https://github.com/gitlabhq/gitlabhq/issues/5636), some servers get a Net::ReadTimeout problem due to a missing parameter in their actionmailer config.
This small fix allows setting the attribute tls by using gitlab_rails['smtp_tls'] = true
.