[APM] apm tracing does not work correctly in Docker Compose/Swarm

[sandys]

This is applicable to Docker Compose and Swarm. This is also connected to support ticket 129543

I have created a replicable Compose testcase here -https://github.com/sandys/datadog-test . This uses a simple containerized python application https://github.com/sandys/datadog-test/blob/master/gunicorn-flask/app/hello.py

This is how I run the python application - https://github.com/sandys/datadog-test/blob/master/gunicorn-flask/Dockerfile#L22
You can also see the various other things I tried there.

This is my compose file - https://github.com/sandys/datadog-test/blob/master/docker-compose.yml

[JohnLZeller]

Bumping this as it seems like a recurring issue