Fix how nevents is read for MG samples and apply MG checks also to aMcAtNlo

Description of bug

• Apparently the way MadGraphUtils prints out nevents changed from

Py:MadGraphUtils     INFO Setting nevents = 11000.0.

to

Py:MadGraphUtils     INFO "nevents" = 10000

which makes logParser crash on recent athena versions

Can @zmarshal @mcfayden @hmildner confirm?
Also is there a better way to extract this from the logs?
One option would be to read it from

05:18:48 10000 = nevents ! Number of unweighted events requested

but it's not very elegant and doesn't match what we do with how we extract the other parameters. If there is no plan to change how this is printed perhaps we can stick to the implementation in this MR (which is not backwards compatible for old releases though).

Changes introduced

• Apply MG checks also for aMcAtNlo samples
• Change how nevents is read from MG samples

Tests

Test on aMC@NLO sample from !372 (merged)

Before fix

After fix

Issues resolved

Closes #