[cern] add cvmfs storage driver config to swarm
Add a new label 'cvmfs_storage_driver' with a boolean value indicating if the CVMFS storage driver should be enabled or not.
Add an additional config resource to setup this driver. For the moment it also does:
- setup docker-ce as an atomic system container, replacing the atomic docker package
- enable 'experimental' in the docker daemon, allowing docker plugins
Eventually this setup will be replaced with upstream reviewed patches.