Update code without configuration update

[werdan]

I have checked in code that currently function update is possible only after update_configuration()
But this means that I have to store all environmental variables values in kappa.yml
Which, in turn means that I can not keep kappa.yml in version control (or I should use Amazon KMS)

It would be nice if to have update_code possibility to just, yeah, update code, not touching configuration.

If it is correct way of thinking I can send a pull request.
Thank you,