Make constrained generators generate more proposals that pass

Currently the constrained generators are pretty unlikely to generate a proposal that gets enacted. Right now all the votes are generated randomly and a large part of the votes are invalid which means that the proposals only get passed in a small percentage of test cases and they usually tend to be `NoConfidence` proposals, because those only need to be approved by DReps.

I think a better way to do this would be the other way around where we decide ahead of time whether a proposal should be passed and then generate the votes accordingly.