Investigate the use of Rspec and ServerSpec

[damien-carcel]

Q	A
Bug report?	no
Feature request?	no
BC Break report?	no
RFC?	no
Affected image and tag	all

Tests are currently ran by a homemade bash runner.

Rspec and ServerSpec seem to be interesting solution to have a real test driver, and apply BDD to the Dockerfiles. They need to be seriously evaluated, by making a POC using them to run the current bash tests.

Example of testing strategy: https://robots.thoughtbot.com/tdd-your-dockerfiles-with-rspec-and-serverspec