Merge remote-tracking branch 'origin/tristan/haproxy-events' into v4.3.1
Bump to 4.3.1
upgrade to cassandra 2.0.8 in travis test

they removed 2.0.7 from the repo
Fix #963 Docker socket timeout
Make UnixSocketHandler as a local url opener only for the Docker check
Docker check try to get container disk size then fallback
Remove Content Length headers when using a proxy

As it seems that some proxy return a 400 when the CONNECT requests has
a content-length header.

(CONNECT requests shouldn’t have it)
Log that we are removing content length header
Separate metadata and agent_checks synchronization
Merge branch 'fix_proxy'
Merge branch 'fix_proxy' into v4.x
Merge branch 'v4.3.1' into v4.x
Merge branch 'master' into v4.x
Let the possibility to disable instance metadata collection

Fix #975
Merge branch 'master' into v4.x
Merge with master
Add socket timeout to Docker check
Do not try to remove Content Length if it's not here
Merge branch 'fix_proxy'
Merge branch 'fix_proxy' into v4.x