Fix CI workflow merge issues

[delner]

Reconciling the changes on master for CircleCI 2.0 with 0.13-dev changes was pretty complicated. This merge commit had a great number of changes, to which I had to add additional bugfixes to, in order to address some problems. This included:

• Missing builds
• An issue with Bundler binstubs that broke dependency loading, particularly in the local Docker environment.
• Rake tests that would randomly fail, depending on test ordering.

There are still some outstanding issues breaking the build on 0.13-dev, and this pull request seeks to resolve those, including:

• Fixing Rubocop issues not addressed in Cleanup Rubocop warnings for spec files #433.