Amazon ECS Agent - Support TaskIAM roles

[sodre]

RancherOS Version: 1.5.4

Where are you running RancherOS? AWS

The current version of RancherOS does not support AWS' ECS TaskIAM roles. This negates one of the biggest advantages of using ECS for managing Tasks and Containers. The fix is not complicated so I submitted three PRs to address the issue:

• rancher/os-services#217: Update the amazon-ecs-agent service to use host networking.
• rancher/docs#2015: Update the documentation page for RancherOS to show the commands for enabling traffic to the Task metadata service, and to disable access to the instance metadata for containers outside of system-docker.
• rancher/os-packer#34: Update the amazon-ecs-optimized image with the documented steps above.

[sodre]

@niusmallnan, sorry to ping you but it is unclear to me what are the contributing guidelines for rancher.

Should I have opened these PRs somewhere else?