Add debug logging showing what is flattened

To make it easier to debug what the flattening
process is doing add a decorator that shows the
result of the translation of tasks/flows into
graphs (and prints a useful summary of what is
in the graph after flattening).

Change-Id: I865bda00a0f192c2497cc35537d8ab654d6e8235
Merge "Add debug logging showing what is flattened"