Create a service check for Agent checks failures
Remove service check from the collector, the check happens in __init__.py
Revert "Remove service check from the collector, the check happens in __init__.py"

This reverts commit ce88af862f248c7e70a38b88c0dc0f1c6306ca36.
Do not send the service check per instance. Only one service check /check
Code cleaning
Update name of the service check
Chnage service check name
Merge branch 'master' into agent-failure-sc
Rename tags "check:" instead of "service:"
Merge pull request #998 from DataDog/agent-failure-sc

Agent failure sc