Don't output to stdout from lib non-interactive methods

It pollutes the test output too much.

Just check for example https://semaphoreapp.com/gitlabhq/gitlabhq/branches/pull-request-8233/builds/1: there are parts of the RSpec where you see nothing but messages like:

    Initialized empty Git repository in /home/runner/gitlabhq/tmp/tests/repositories/group336/gitlab.git/

If anyone misses the messages, please patch to log them instead. This can be done with `popen` as well.