Adding service_check to the HTTP and TCP checks

A check is present to be able to ignore the events that these checks submit, so that when people migrate to the serverside service_checks, they can avoid duplicate events.

Regarding the tags [here](https://github.com/DataDog/dd-agent/commit/9d5680de278c22351bce6780ee8ac0e4d3aa56d2#diff-1e218dd5b800bab577b2965306341428R157), should I just use the host where we point the checks as the hostname, instead of creating a new tag target_host?

Ok, I'll make the change and update the other ones while I'm at it.