* Add rubocop linting to docker:test rake task
* Add eslint JS listing to plugin files, and add SKIP_LINT variable
* Fix failing ‘polls’ plugin eslint
Using eslint-disable-line, as is done in core qunit tests such as `acceptance/group-logs-test.js.es6`
* Add plugin test eslint to travis config
* Merge some eslint lines
* Allow running specific plugin tests using ENV variables
* Add a `rake plugin:qunit` task to match the existing `rake plugin:spec` task
* Improve docker.rake to allow running specific plugin qunit tests
* Purge cache before and after qunit tests
* Stop module auto-loader trying to auto-load tests
* Use URL query parameters to pass config into Qunit, avoiding caching issues
* Oops, searchParams doesn’t work in phantomJS. Parse the URL manually.
* Escape ampersands before passing URL to phantomJS, otherwise multiple parameters go wrong
