refs https://github.com/TryGhost/Team/issues/728
- In additions to easier tracking of "this" context in the unit tests it gets rid of unnecessary Bluebird's "reflect" method which was making unit test dependent on Bluebird's specific Promise implementation
refs https://github.com/TryGhost/Team/issues/728
- This is a first step before moving update check code into an outside codebase.
- The aim is to have a self-contained module which could be unit tested and have a very clear API