How to set up a RancherOS CI on an ARM docker host

Drone CI Setup Instructions for ARM/ARM64

These are almost exactly the same as for the regular Drone CI, with only a couple differences:

1. Drone CI server docker image

Use armhfbuild/drone:0.4 as the Drone CI server image. Should run fine on ARM (like Raspberry Pi 2) and ARM64 (like Estuary D02) docker hosts.

2. arm/arm64 rancher/dapper image

Make sure you've done the following before having Drone run RancherOS builds. Run against the same docker daemon you're running Drone with:

docker pull rancher/dapper:1.10.3_arm
docker tag rancher/dapper:1.10.3_arm rancher/dapper:1.10.3

This is necessary because .drone.yml syntax does not support choosing the image based on the host platform. The actual rancher/dapper:1.10.3 image on DockerHub is for amd64 (x86_64), so your builds won't run if you don't do that.