Get basic artifacts movement working (this has a number of issues to discuss!)

Issues:

- Right now, the "outbox" is .winchman/out and the "inbox" is .winchman/in/{previous-unit-id}. These are currently hardcoded, but we should make them configurable (requires a change to the graph-builder)
- Because of the hard-coded nature of above, Dockerfiles have to create the ".winchman/out" directory themselves.
- This depends on a change to the builder-core to not delete temporary images (PR #20)
- This depends on a change to the builder-core to always log the image_id (PR #21)
- The copying of the log code to pull out the image_id is ugly. This code is temporary, and we need to figure out a nicer way.
- appendBuildArtifacts has to currently move the 'out' directory. Artifactory should be updated to allow us to specify a prefix to be removed
You should not be using the log entries to determine any important information, as the log entries may change.  Instead, use the status messages, as that is their intended purpose.