Fixed tests to not plot data.
Fixed tests to not plot data.

I use plots for when I run the tests, but they should be turned
off by default so that py.test will not generate plots.

aitatanit/filterpy,Censio/filterpy,rlabbe/filterpy,Censio/filterpy,BrianGasberg/filterpy,rlabbe/filterpy,aitatanit/filterpy,BrianGasberg/filterpy