CITest: migrate Trigger_athena_MC test
Migrate the Trigger_athena_MC test from TestConfig to CITest. Drop the usage
of the runTrigCI.py
wrapper script as these functions (e.g. private run directory) are taken care of by CITest already. This only affects the master branch. Both new and old job will run in parallel for a few days. Migration of the other trigger tests will follow.
Relates to ATLINFR-4360. cc @vmartin @okumura @rbielski @tbuanes