Output dependency graph to identify source of bad license that triggered fails-on.

[shengy90]

For instance I'd like to flag GNU/ GPL licenses in my dependency.

Right now --fail-on fails on the first instance of a dependency that uses GNU/GPL license. The only way to troubleshoot right now is to:

• Use alternative library like https://github.com/tox-dev/pipdeptree to detect how this dependency come about in the first place, then uninstall the source dependency
• Or uninstall it one by one until no more flags are raised which is not a good solution.

It'd be great if we could identify all failed dependencies (not just the first one) and identify the sources so we can get rid of the incompatible ones!