Latest release of jenkins-job-builder is now attempting to delete old
Jenkins views when updating but this new code triggers an exception when
deploying jobs on our Jenkins instance, so add option --jobs-only to
jenkins-job update command as a workaround to restore previous behavior.

With a potential docker agent.

Some docker jobs can run directly on the host machines but some cannot. The ones
requiring some mount points to be passed along for example. In that case, the docker
agent is preferred.

Ref. swh/infra/sysadm-environment#4724

Ref. swh/infra/sysadm-environment#4724

Remove use of setup wizard as plugins have already been installed.

This also removes the need for authentication in that sample Jenkins
instance.

Currently, the only way to test Jenkins configuration changes using
docker is to push changes to a remote feature branch in swh-jenkins-jobs
repository and make jenkins clone that branch to test the changes.

This is not really convenient to quickly test changes so prefer to
mount the local swh-jenkins-jobs repository as a docker volume
and clone that repository from Jenkins filesystem.