Create a plugin interface for sandboxes?

Issue spawned off from #39 :

Stefano said:

Sadly it seems that using isolate is a bit cumbersome, especially due to system behaving not as expected or having different configurations. I am confident that most of these problems will be solved by time as Linux 3.8 will gain more market share, but nonetheless it seems that isolate is more dependent on the distro.

What I am worried about is that, especially in this transition time, some users will try CMS and fails because of problems connected to run isolate. On the other hand, to try CMS out, or to organizing contests whose contestants are trusted, they might even avoid the use of a sandbox at all.

The proposal is to consider writing a standard interface for sandboxes, in such a way that people not currently interested in having a strong security can use a the "void" sandbox, and possibly (if it does not involve a lot of work) we could keep mo-box as a backup.

I think this would be useful, but not as useful as having isolate work better, so I don't want to lose resource on the latter to improve the former. Maybe I'd just ask you to keep in mind the possibility of having a modular sandbox system while you are working on improving isolate.

Start by reading issue #39 and tracing how the current isolate sandbox is integrated. Review the existing isolate and mo-box usage, then establish the scope and acceptance criteria for a modular sandbox interface, including whether a void sandbox is supported.