Fix wrong secret code generated after a364c96980de549e24a397263136d518098ce9c4 change

a364c96980de549e24a397263136d518098ce9c4 was missing injection of steps.
This change introduces a factory that does the same thing SensioDistributionBundle does at boot time.
Merge pull request #438 from ezsystems/secret_fix

Fix wrong secret code generated after #412