Utilizing the checks API to report the build state to Github provides
some additional functionality that is not supported by the status API.
Those are:
- Defining custom actions to e.g. cancel a running build
- Report line-based file annotations
This change implements the basic checks API workflow. Once this is in
place, the additional features could simply be added on top.
Change-Id: I7e790783ee35971085863b5487ff094fa0b23d65
Story: 2007268
Task: 38672
33f87bea9c