Dependency graph builds could be slightly smarter with disambiguation

[mmitche]

In case multiple builds match the same sha when building a dependency graph, and maestro doesn't know which is actually in use in the repo, it may be possible to do some more disambiguation based on other files:

• If assets are only produced by one of the builds, eliminate it from contention
• Look at other assets in the version.details file that are on the same file. If any are not ambiguous, choose that instead.