Ensure that tracing max_depth works as expected with country-template

[bonjourmauko]

Hi there!

I really enjoy OpenFisca, but I recently encountered an issue.

Here is what I did:

openfisca test

Here is what I expected to happen:

For the max_depth option to be set to a default reasonable amount of 3 or 5.

Here is what actually happened:

It is set to sys.maxsize which is unreasonably big.

Here is data (or links to it) that can help you reproduce this issue:

Take a look at the option in test_runner.py and implementation in tracers module.