(Ersetzt) Plugin-Continuous-Integration-Tests auf Travis CI einrichten

@david This script didn’t work for me out of the box. Is there any other config it assumes?

It fails in Travis with

The command "docker run -e "COMMIT_HASH=origin/tests-passed" -e "SKIP_CORE=1" -e SINGLE_PLUGIN=$plugin_name -v $(pwd):/var/www/discourse/plugins/$plugin_name discourse/discourse_test:release" exited with 1.