Print all buffers in case of error

[nobrakal]

Hi,

While working on another issue, I hit the exact same than described in #232 : In the webapp, the grading fails with:

Erreur dans l'exercice lors du test de la solution utilisateur

And no other information.

So I decided to give it a try, and discovered that a buffer which contained some logs was not printed (and it was indeed the one where was the information I needed).

This PR fix this problem.

Fixes #226
Fixes #232

[nobrakal]

Note, this also fix in part #226 , since the report also print now if an exception was raised by the student code.