Sweeping !457 from Rel-v34r0 to master. CI: add DIRACOS_VERSION to CI script and CVMFS installation instead of latest

Ghost Userrequested to merge
cherry-pick-2-df1b7a3f-master into master

CI: add DIRACOS_VERSION to CI script and CVMFS installation instead of latest

See merge request !457 (merged)

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