Track ArtifactBuild's original_nvr and rebuilt_nvr. Fixes bad koji_parent_nvr value when rebuilding container images.
    
    - Add `original_nvr` and `rebuilt_nvr` to ArtifactBuild.
    - Change the ErrataAdvisoryRPMSSigned handler to set `build.name` to name part of NVR,
      `build.original_nvr` to NVR and to generate `build.rebuilt_nvr` using new
      `utils.get_rebuilt_nvr()` method.
    - Properly set the NVR of parent images to `build.rebuilt_nvr` instead of using
      original NVR.