Properly handle testing using dependency

Usage of the fog gem requires we have fog installed. Using et_fog is one
way to handle that.
Convert specs to RSpec 3.0.2 syntax with Transpec

This conversion is done by Transpec 2.2.4 with the following command:
    transpec -f

* 1 conversion
    from: obj.stub(:message)
      to: allow(obj).to receive(:message)

For more details: https://github.com/yujinakayama/transpec#supported-conversions