Speed up tests

[mvz]

Summary

Aruba's tests take too long. Especially on JRuby, but on MRI they're still take quite long. Let's make them faster.

Possible Solutions

• Test edge cases as unit tests instead of using an end-to-end test. This will probably mean moving them from cucumber to rspec.
• Figure out a way to reduce indirection. Current feature tests often do a nested cucumber run, which itself does a nested run of some Ruby program.

Steps to Reproduce (for bugs)

Look at a typical Travis build.

Context & Motivation

Development is slow when you need to wait that long for a build to finish.