Proposed changes to discourse-setup because Digital Ocean blocks outbound smtp

[nathank (Nathan Kershaw)]

@pfaffman

I propose these changes to discourse-setup

• changing default SMTP port for those services to 2525.
• adding a test (e.g., nc -z -w5 smtp.mailgun.org 25) to see if the chosen SMTP port is open

Why those 3 services services? They’re the ones that discourse-setup currently knows about and recommends smtp_user_name for).

With the recent decision by DO to block port 587 for all new droplets, perhaps it is time to revisit this.