Do not suppress tracebacks when running 'test' notebooks via nbval

[willfurnass]

At present tracebacks are suppressed via the logic in init.py. This is annoying when pytest fails.

A possible solution: if there is an active IPython session then only suppress tracebacks if an env var is defined and set to 1. This env var could then be set to 1 in tox.ini

[jarmarshall]

I think this is setVerbose()? Add this to test notebooks if it's not there already?

[willfurnass]

It's the user manual Notebook that this would be most useful for as it's the first Notebook to be run by tox but I presume you don't want setVerbose(True) added to that Notebook.

[jarmarshall]

OK - maybe run it last? It's good to test the user manual of course, but most of the functionality should have been tested if the other notebooks complete...