Include tags with http service check

[bakins]

This makes each check searchable for events, etc, by tag rather than having to tag the host.

[remh]

Thanks @bakins !
We should probably also add the url as a tag as we do for the response time metric
https://github.com/bakins/dd-agent/blob/c781e021b924d352d250e8b0e9e60d43789856f0/checks.d/http_check.py#L58-L60

Can you add that?

[bakins]

Added. currently untested. Should maybe do that in a helper function as we have same logic in two places

[remh]

Thanks!