Put back SocketError in the common rescue clause for SubscribeUserJob.

It turns out there is no need for SocketError to have a separate rescue. The SocketError I'm getting in staging is raised when trying to send a notification email from the job; this happens in the ensure clause, outside of the scope of the rescue clause.
The environment file (staging.rb, production.rb) is copied into the deployment in the background servers, as well as the web servers.

This is necessary because this file has the SMTP configuration necessary to send emails through Amazon SES. The web server needs to send emails related to authentication and signup, but the background server also needs to send emails to notify the user when the OPML import has finished.