Travis CI migration to Gitlab CI

[bourtemb]

This repository is using Travis CI.

At the beginning of January 2021, CI using Travis CI projects still on travis-ci.org will no longer work.
To avoid migrating to travis-ci.com which is less friendly with Open Source projects like tango-controls, the Tango Steering Committee decided to migrate the tango-controls git repositories to gitlab.com and to use Gitlab CI for the Continuous Integration.

In order to prepare the migration, CI for this repository should be migrated to gitlab-ci and tested.
To work on that topic before the official migration, one could work on a fork under https://gitlab.com/tango-controls/test_gh_import gitlab group.