Add unit tests for shinyapps.io deploys

[mslynch]

[aronatkins]

There are a number of tests showing how to use webfakes to stub services.

[hadley]

@mslynch are there any areas that you think are particularly important to begin testing?

[mslynch]

I'd start with the simplest happy-path case, just bundling/creating/deploying an app.