Suppress the logging of the seed fetch by default

Add in handling of a task argument for the fetch task so that if the
logging is needed, you can run `rake db:seed DEBUG=true` or `rake
db:seeds:fetch DEBUG=true` in order add the logger to the Faraday
middleware stack.
Merge pull request #1676 from mattr-/silence-faraday-when-fetching-seed-data

Suppress the logging of the seed fetch by default