Add tests in Travis with Gazebo 10

[traversaro]

With the current structure, this means adding gazebo10 support in https://github.com/robotology-playground/docker_images/blob/master/robotology-tdd/Dockerfile, or change the system to use some vanilla docker image, and install gazebo & yarp autonomously, as done for example in https://github.com/robotology/gazebo-fmi/blob/master/.ci/install_debian_and_script.sh .

[traversaro]

If we switch to use our own image, we can also go back to check compilation against Gazebo7, see #433 for a related issue.

[diegoferigo]

After more or less 2 years of usage, I came to the conclusion that using generic docker images for CI as the ones provided by robotology/docker_images is applicable only in particular cases. Often it is easier vendoring the CI docker image within the same project repository. The trade-off is that project maintainers have to edit individually all the images in case of an update that requires manual modification.

In the vendoring case, I found that a good solution to build images while minimizing manual effort is exploiting cron-based CI jobs. You can find an example here.

[traversaro]

I totally agree.

[traversaro]

The CI has been migrated to GitHub Actions in #453 and further improved (with support for testing Gazebo 10&11) in #496 . This issue can be closed.