ATR-27398: Fix L1Defined test and correct menu errors
Addresses:
- L1Defined test not catching all cases of HLT chains without their L1 items defined in the corresponding L1 menu
- CI errors from HLT menus (lowMu, HI) containing such chains
@fwinkl I still don't know why this wasn't consistent in CI or locally, but now I just set an empty input file list and trigger L1 json creation when needed. As a bonus now we can correctly check multiseed L1 items.
@dguest, this is so you know I got rid of the janky error parsing. So exceptions in the parsing will now break the script, but before I changed that there were reliably 0 'known errors'. Other options should still be fast + seem to work. L1 check might be marginally slower but works properly.