Allow CI to run with external LHE inputs

Changes introduced

• Use rucio get to download external LHE files in CI job
• Allow Gen_tf to run with --inputGeneratorFile pointing to the downloaded file if inputGeneratorFile is provided in the log
• Switch from atlas/*-atlasos to atlasadc/grid* images since rucio wasn't working in the former

Todo

• Test with multiple external files

Successful check with one job with a single LHE and one with multiple LHEs here: https://gitlab.cern.ch/atlas-physics/pmg/mcjoboptions/-/pipelines/2537878

Tests

With slc6

Here: https://gitlab.cern.ch/atlas-physics/pmg/mcjoboptions/-/pipelines/2532783 Notice that athena runs and it's the logParser that fails. This is expected (tested locally). IIRC the printout of the number of input files was added later than the release used in that jO.

With cc7

Here: https://gitlab.cern.ch/atlas-physics/pmg/mcjoboptions/-/pipelines/2529083

Issues resolved

Closes #64 (closed)