Avoid doing repair:database in test because can really take long time

The ProblemClearer launch a repair:database to limit the size of mongoDB
database. Avoid to do it in test because can take 3s.

This commit reduce by 3s the spec suite
Not require 'rake' in test suite

To test the rake db:seeds task require the db/seeds.rb file instead of
require 'task' and launch the task.

Avoid useless output on test to stubing Kernel.puts