Create test running all demos

[Martin Sandve Alnæs]

This will be a long one, if we have a parameter --short to the test system we can set time to a small value just so we can execute every demo a little bit.

[Øyvind Evju]

I guess this won't be part of the py.test-suite? We have a script for running the demos that I guess would be sufficient for the buildbot to run?