Add /cvmfs/cms-opendata-conddb.cern.ch to /etc/cvmfs/default.local

[katilp]

/cvmfs/cms-opendata-conddb.cern.ch needs to be added in order to be able to use the same commands as in the docker and cmssw pre-exercises:

• https://cms-opendata-workshop.github.io/workshop-lesson-docker-preexercises/05-validation/index.html
• https://cms-opendata-workshop.github.io/workshop-lesson-cmssw/05_configuration/index.html

[katilp]

And cms-bril.cern.ch as well for brilcalc to work

[clelange]

@katilp should be fixed, reopen if not.