Disable the default jobs included with the gem

[jgeiger]

Added a config flag to turn off the default jobs included with the gem since they're only good for examples.

https://github.com/jgeiger/cloud-crowd/commit/3adfa3873058dd087de13274387a9e7e032a4b3a

[jashkenas]

Thanks. I've just merged your branch, including the previous commits.