fix: change default setting of SMTP_SSL

[danone-dev]

This fixes #537
Changed the default of SMTP_SSL to 'not set'. Also update the redmine_configure_email_delivery function so it removes the ssl: line from configuration.yml if no SMTP_SSL environment variable is set.

If you need SMTP_SSL: true you would have to set the variable anyway, even in the old situation.

[jcormier]

I gather ssl: false is not a valid setting then? You don't outright say it but it seems implied by your change.

If that's the case, then I'd prefer we invert this check and delete this setting if it's set to anything but true. That way if someone sets the ENV variable to false, it still works correctly.

if [[ "${SMTP_SSL}" != "true" ]]; then

[danone-dev]

The only thing that has changed now is that SMTP_SSL: true will end up in the config, and SMTP_SSL: false will be removed from the config. The default remains SMTP_SSL: false, so the README and env-defaults don't have to be modified.

[jcormier]

Do you need this backported to a previous release?

[danone-dev]

No, this is fine for me. Thanks.