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?

Do we have a standard way for this to reflect default value in the examples?
I based my self on the rest of the file (see [conf](https://github.com/DataDog/dd-agent/blob/rudy/http-tcp-service/conf.d/http_check.yaml.example#L26-39)) where the commented value is the opposite of the default so that people just have to uncomment to switch the behaviour.

Not sure which one makes more sense