Avoid db:dev_seed log print when run from its test

The db:dev_seed rake logs info as it progresses as information for the
developer. But that's not needed when ran from its tests file, and it
bloats the travis/rspec output with unnecessary information.

Now the task will always log info unless the rake task receives an
optional argument.

db/dev_seeds.rb

@@ -1,7 +1,9 @@
 require 'database_cleaner'
 DatabaseCleaner.clean_with :truncation
 @logger = Logger.new(STDOUT)
-@logger.formatter = proc { |_severity, _datetime, _progname, msg| msg }
+@logger.formatter = proc do |_severity, _datetime, _progname, msg|
+                      msg unless @avoid_log
+                    end
 
 def section(section_title)
   @logger.info section_title