remove unused variable
fix missing yaml_db task issue…

- yaml_db rake task is implemented in such a way
  that we can't just require it like with the
  airbrake task.

- Just adding the gem as dependency to shoestrap
  does not solve the issue

- Therefore making sure yaml_db is in the gemfile
  and is no longer a dependency of shoestrap
  directly.
refactor tasks, make it work with any env