Changed default timeout of smtp from 10s to 60s.

Summary:
Our smtp server responded slowly sometimes and reached the timeout, but actually
it had sent the email successfully. The mta then retried and sent duplicated
emails. So changed to a bigger default value.

Test Plan: Tested in our deployed and it worked

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D8852