Clean up specs - lets vs instance_variables

[eaierstuck]

We should decide on if we are using lets or before blocks for our specs...

This article makes an argument for using lets unless it is a before_all block (https://www.ombulabs.com/blog/rails/rspec/ruby/let-vs-instance.html)

• Convert all @instance_variables in before blocks to lets

[jtwhittington]

Done in #64