TECH-16: WIP - visual regression tests with backstop JS

[enotick]

@mikemccaffrey @RobLoach I made a first attempt to integrate backstop.js into the circle. I need some help on:

• testing strategy for this PR
• verification on implementation
• test scenarios (for now only homepage)

My idea:
we only run test workflow when we merge / push to a branch visual - since we don't need to run it all the time on every deploy

I am not sure how to best test these changes perhaps the best would be try it on one of the projects and see if there are any problems. I took the config that was advised on Pantheon community forum. https://discuss.pantheon.io/t/backstopjs-with-our-pantheon-circleci-orb/386/6

[enotick]

@RobLoach @mikemccaffrey I got it working - more details in the Jira issue.

[RobLoach]

Looks great! If you add some documentation with some instruction on how to get it up and running, and where to check tests, that would help the rest of the team get on board.

[enotick]

Looks great! If you add some documentation with some instruction on how to get it up and running, and where to check tests, that would help the rest of the team get on board.

@RobLoach more details with how to run is in the issue - but I'll also work on the documentation we can put into the wiki :)