Issue with unit test CNN

[glemaitre]

@dvro @chkoar I already saw an issue with the unit test of the CNN method. The recurrent call to the KNN lead to a memory allocation problem I think. In fact, the test finish with an unexpected:

Fatal Python error: deallocating None
build_tools/travis/test_script.sh: line 27:  3501 Aborted

I don't think that his error is from our module. It should come from either scikit-learn or numpy/scipy.
Could you also have a look at it.

Note that I disable it in the PR #112 since that the method can still be used.

[dvro]

@glemaitre were you able to replace this error on your machine?

[glemaitre]

nop only on travis

[glemaitre]

This is issue will be addressed with the new toy testing #118