Validation of pLHE should check the total number of events

[lmoureaux]

Validation of pLHE requests should go to all events, this is to make sure that we can read LHE until the end of the file, and No. of events are the same as requests. Larger no. of events in a request will lead to an empty file which causes the issue in production.

We need mechanism to pLHEGEN validation also.

From cms-PdmV/cmsPdmV#1073