add another file to detect platform type

Amazon Linux distributions may not include a redhat-release file.
Add message rate metrics to RabbitMQ check.

This is useful when you have a queue that's consumed very quickly. In
this case the Agent will always/nearly always report 0 for queue sizes.

New metrics:
    - `rabbitmq.queue.messages.rate`
    - `rabbitmq.queue.messages_ready.rate`
    - `rabbitmq.queue.messages_unacknowledged.rate`
More rabbitmq metrics
Fix a typo in the rabbitmq metrics.
Do not try to bundle pup.html
Mock the sleep by modifying collection time
Merge pull request #1157 from DataDog/leo/flakycollection

Mock the sleep by modifying collection time
Remove max_containers limit for Docker check
Cleanup Docker example config file
Add socket_timeout parameter to Docker check
Make the container size collection configurable
Remove warning when no containers are running
Make event creation in Docker check optional
Revamp Docker events: aggregate, put details in the body, add container name
Tag docker.containers.running by image
Drop docker.total_* metrics because it is not used and meaningless
Update CHANGELOG.md
Bump version to 5.0.4
Update CHANGELOG.md
Update CHANGELOG.md