[ci] Avoid duplication of basic running test
Created by: nemesisdesign
These lines seem duplicated:
- https://github.com/openwisp/ansible-openwisp2/blob/master/.travis.yml#L31
- https://github.com/openwisp/ansible-openwisp2/blob/master/.gitlab-ci.yml#L16-L19
Maybe we can extract those lines in a script that gets called by both CI systems