Use right parent image if parent image changes during child image releases.
    
    Consider following situations:
    
    - `foo-1-1` has `x-1-1` parent image.
    - `foo-1-2` has `y-1-1` parent image.
    - `bar-1-1` has `foo-1-1` parent image.
    
    When Freshmaker generates the list of images to rebuild, the current code
    does not handle the case when older `foo` image was built against `x-1-1`
    and newer `foo` against `y-1-1` well. It will generate following list:
    
    - `bar-1-1` will be rebuilt against `foo-1-2`, because `foo-1-2` is the latest release.
    - `foo-1-2` will be rebuilt against `x-1-1`, because `original parent of `bar-1-1` was
      `foo-1-1` and it depended on `x-1-1. This is wrong. In fact, it should be built against
      latest release of `y` which is `y-1-1`.
    
    This PR fixes this problem by introducing another initial phase in code which
    deduplicates images to rebuild.
    
    In this phase, Freshmaker will search for cases when older image has different
    parent than the newer image and if it finds such case, it will replace the
    parents completely according to latest image, because we will in the end
    use the latest image.
    
    In our example, it will do following in this initial phase:
    
    - It finds out that `foo-1-1` has different parent than `foo-1-2`.
    - It knows that `foo-1-2` is latest, and therefore it will change the
      `foo-1-1` parent of `bar-1-1` to `foo-1-2`, include its dependency
      on `y-1-1`.
    
    After this initial phase, the `bar-1-1` will have `foo-1-2` dependency.
    This will make Freshmaker to generate proper list of images to rebuild.