Fix "lost" notifications when submitting multiple passive checks - for volatile service only

I have noticed that current shinken code does not allow to process EVERY check result - which is ok obviously. But it also did not process volatile service check results as I expected. I would expect that volatile service accept every notification - even if they are sent multiple times per second. Currently that is not the case.

Shinken Team - please review and pull this commit if you want. Just note that I used copy.copy() when creating Notification template and I am not conviced that this is elegant. But it was because the schedilingitem was overwriten by subsequent check results.

I just don't more time to spend on this issue.