Update haproxy events

- add haproxy agent name in the title
- add backend in the tags
- align with metrics tags
Catch docker socket timeout, fix cpu metric as a rate
Fix typo, better exception message for Docker
Turn Docker total_ metrics of by default, add flag
Fix docker exception catching, rename `total` config option
Merge pull request #964 from DataDog/docker_check_adjustment

Docker check adjustment
Merge pull request #960 from DataDog/tristan/haproxy-events

Update haproxy events
Update CHANGELOG according to 4.3.1
Merge branch 'master' of github.com:DataDog/dd-agent
Update CHANGELOG.md
Improve the change log
4.3.1 is not released yet
4.3.1 is out
4.3.1 is out
Merge branch 'master' into omnibus_bundling