change test exception handling to actually work

exceptions occurring inside the test framework when in parallel aren't handled properly, and cause the framework to hang.
<a href='#crh-start'></a><a href='#crh-data-%7B%22approved%22%3A%20%7B%22https%3A//github.com/conslo%22%3A%20%7B%22avatar_url%22%3A%20%22https%3A//avatars.githubusercontent.com/u/450860%3Fv%3D3%22%7D%7D%2C%20%22comments%22%3A%20%7B%22General%20Comment%22%3A%20%7B%22html_url%22%3A%20%22https%3A//github.com/Spentry/tmwy-lettuce-parallel/pull/8%23issuecomment-63540990%22%2C%20%22comments%22%3A%20%5B%7B%22body%22%3A%20%22%3Ashipit%3A%20%22%2C%20%22created_at%22%3A%20%222014-11-18T20%3A41%3A35Z%22%2C%20%22user%22%3A%20%7B%22avatar_url%22%3A%20%22https%3A//avatars.githubusercontent.com/u/450860%3Fv%3D3%22%2C%20%22html_url%22%3A%20%22https%3A//github.com/conslo%22%7D%7D%5D%2C%20%22title%22%3A%20%22General%20Comment%22%7D%2C%20%22Pull%20236d657feeb64ac994d2df344ec17bfa884e0133%20lettuce/__init__.py%207%22%3A%20%7B%22html_url%22%3A%20%22https%3A//github.com/Spentry/tmwy-lettuce-parallel/pull/8%23discussion_r20538095%22%2C%20%22comments%22%3A%20%5B%7B%22body%22%3A%20%22this%20is%20a%20problem%22%2C%20%22created_at%22%3A%20%222014-11-18T21%3A06%3A35Z%22%2C%20%22user%22%3A%20%7B%22avatar_url%22%3A%20%22https%3A//avatars.githubusercontent.com/u/450860%3Fv%3D3%22%2C%20%22html_url%22%3A%20%22https%3A//github.com/conslo%22%7D%7D%2C%20%7B%22body%22%3A%20%22%3A%2B1%3A%20%22%2C%20%22created_at%22%3A%20%222014-11-18T21%3A07%3A59Z%22%2C%20%22user%22%3A%20%7B%22avatar_url%22%3A%20%22https%3A//avatars.githubusercontent.com/u/450860%3Fv%3D3%22%2C%20%22html_url%22%3A%20%22https%3A//github.com/conslo%22%7D%7D%5D%2C%20%22title%22%3A%20%22File%3A%20lettuce/__init__.py%3AL222-230%22%7D%7D%2C%20%22processed%22%3A%20%5B%22https%3A//github.com/Spentry/tmwy-lettuce-parallel/pull/8%23issuecomment-63540990%22%2C%20%22https%3A//github.com/Spentry/tmwy-lettuce-parallel/pull/8%23discussion_r20538095%22%2C%20%22https%3A//github.com/Spentry/tmwy-lettuce-parallel/pull/8%23discussion_r20538192%22%5D%7D'></a>
<a href='https://www.codereviewhub.com/'><img src='http://www.codereviewhub.com/site/github-bar.png' height=40></a>

<img src='http://www.codereviewhub.com/site/github-approved-avatar.png'><a href='https://github.com/conslo'><img src='https://avatars.githubusercontent.com/u/450860?v=3' width=34 height=34></a>

- [x] <a href='#crh-comment-Pull 236d657feeb64ac994d2df344ec17bfa884e0133 lettuce/__init__.py 7'></a> <img src='http://www.codereviewhub.com/site/github-completed.png' height=16 width=60>&nbsp;<b><a href='https://github.com/Spentry/tmwy-lettuce-parallel/pull/8#discussion_r20538095'>File: lettuce/__init__.py:L222-230</a></b>
- <a href='https://github.com/conslo'><img border=0 src='https://avatars.githubusercontent.com/u/450860?v=3' height=16 width=16'></a> this is a problem


<a href='https://www.codereviewhub.com/Spentry/tmwy-lettuce-parallel/pull/8?mark_as_completed=1'><img src='http://www.codereviewhub.com/site/github-mark-as-completed.png' height=26></a>&nbsp;<a href='https://www.codereviewhub.com/Spentry/tmwy-lettuce-parallel/pull/8?approve=1'><img src='http://www.codereviewhub.com/site/github-approve.png' height=26></a>&nbsp;<a href='https://www.codereviewhub.com/Spentry/tmwy-lettuce-parallel/pull/8?approve=0'><img src='http://www.codereviewhub.com/site/github-undo-approve.png' height=26></a>&nbsp;<a href='https://github.com/Spentry/tmwy-lettuce-parallel/pull/8'><img src='http://www.codereviewhub.com/site/github-refresh.png' height=26></a>
<a href='#crh-end'></a>
:-1: