Examine slow-loading dependencies

[mvz]

Summary

Some of Aruba's dependencies take a longish time to load. We pay for this time in every cucumber scenario. We should examine
whether we need each of them.

Details

At least the following are 'slow'. Note: In normal use this would be insignificant, but in our tests this adds up, especially for JRuby:

• contracts
• tempfile

Context & Motivation

Ongoing attempts to speed up the test suite.