tools: Moving grapher to tools

There is no need to keep grapher at the root directory
cardiff: Initial import

The cardiff tool is about finding commonalities and differences between
traces reported by the benchmarking tool (health-test)
cardiff: Code refactoring

Let's move many functions from cardiff.py to utils.py to get them used
by the testing tool. This make also the main program easier to read.
cardiff: Adding nosetests

Adding nosetests inside cardiff to make it more robust