Add screenshot on failure

[KaptenJansson]

Description
When debugging issues that only occur on travis it would be really helpful if we could grab a screenshot of the error and make it view-able somewhere.

• Add screenshot handling in src/js/selenium-lib.js using Webdriver api's (does not look like this is part of the Javascript api, need to investigate this further)
• Store the file on the travis bot and then upload it S3, documentation here: https://docs.travis-ci.com/user/uploading-artifacts/
• Include the link to the screenshot in the travis output

[fippo]

driver.takeScreenshot().then((img, err) => {

combined with fs.writeFileSync solves the first part.