Created EPOS4 external example generator

[jackal1-66]

In order to run on hyperloop an external generator based on the automatic FIFOs mechanism has been setup for EPOS4.
The generation has been tested locally using this example command

o2-sim-dpl-eventgen --generator external --nEvents 1000 --aggregate-timeframe 2 --configFile $O2DPG_MC_CONFIG_ROOT/MC/config/examples/ini/GeneratorEPOS4.ini -b | o2-sim-mctracks-to-aod -b | o2-analysis-mctracks-to-aod-simple-task -b

or changing the parameters with

o2-sim-dpl-eventgen --generator external --nEvents 1000 --aggregate-timeframe 2 --configFile $O2DPG_MC_CONFIG_ROOT/MC/config/examples/ini/GeneratorEPOS4.ini --configKeyValues "GeneratorExternal.funcName=generateEPOS4(\"my/path/example2.optns\", 1000)" -b | o2-sim-mctracks-to-aod -b | o2-analysis-mctracks-to-aod-simple-task -b

It is important that in the optns file the option set ihepmc 2 is set, otherwise the generation won't work (as specified also in the HepMC EPOS4 generation tutorial).

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[jackal1-66]

I checked again the modifications and I didn't find any issue. I retested everything thoroughly both locally and on LXPLUS and the test passed successfully. I think the issue might be either related to the slc7 build, or to issues when creating the automatic FIFO with the child spawning of EPOS4. Unfortanately I am not able to say more since I don't have access to the CI machines.

[jackal1-66]

Issue with CI is related to the fact that the environment variables seem not to be set correctly in the docker. This can be easily fixed by editing the running script (since it seems instead that EPOS4_ROOT is set correctly). Adding this check and variable exports in epos.sh fixed the test that is now working fine. Merging since the CI check passed. As a note, the problems could be reproduced in lxplus (or locally) by simply unsetting EPO4, HTO, CHK and OPT.