log lines from DAG walking should not appear

[BrianHicks]

since changing to AcyclicGraph.Walk from AcyclicGraph.DepthFirstWalk, we're getting some debug log spam. This needs to be taken care of in the root cmd. We probably should just switch to the stdlib logging package and drop logrus because of this.

[langston-barrett]

What's the motivation for dropping logrus? Can we not just add a flag (maybe --log-level) that defaults to info or warn and set the logrus level from there?

[BrianHicks]

Terraform uses the default logger. We're using their DAG. We'd have to redirect it in awkward ways. Better to just adapt for now.