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:

• Force aws-ecs-agent to use the host networking os-services#217: Update the amazon-ecs-agent service to use host networking.
• Add instructions for secure AWS Task IAM Roles 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.
• Add Amazon's TaskIAM configuration to ecs image 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?