Redesign of CI for simplification

The major problems seen in the "alpha" tests were:

1. Multiple commits with failed pipelines would be considered mergeable if the final commit just happened to pass the pipeline
2. Users had to remember to specify [skip modfiles] when changing files in their branch - this should not be necessary
3. Failed athena jobs related to eos access (#38 (closed))
4. Running automatic script not intuitive

The following should simplify the usage of the CI

• Make jobs run for all commits (this would solve #36 (closed)) - apparently the only:changes and only:merge_request logic still suffers from logical flaws, so avoiding them would make the interpretation of the pipelines easier: if it's green it can be merged, it it's red it can't
• Avoid the need to specify [skip modfiles] if a commit changes things which are not in the master #20 (closed) - this should make the usage more straightforward and for normal commits no fancy commit messages would need to be specified
• Create image atlas/atlas_external_cvmfs and gitlab-registry.cern.ch/atlas-physics/pmg/mcjoboptions:eos_bash - this would solve #38 (closed)
  • Global cache with above image to be shared across all jobs #7 (closed) (moved to #7 (closed) so closing)
  • When this is in place it would be trivial to incorporate the work by @mukumar