roles/docker: Install and set up Docker daemon

The *docker* role configures the Docker daemon on the managed machine.

roles/docker/files/generate-docker-key.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+set -ex
+
+: ${DOCKER_SVC:=${1:-docker}}
+
+dropin=/etc/systemd/system/${DOCKER_SVC}.service.d/protect-system.conf
+
+systemctl stop ${DOCKER_SVC}
+if [ -f ${dropin} ]; then
+	mv ${dropin} ${dropin}.disabled
+	systemctl daemon-reload
+fi
+systemctl start ${DOCKER_SVC}
+test -f /etc/docker/key.json
+systemctl stop ${DOCKER_SVC}
+if [ -f ${dropin}.disabled ]; then
+	mv ${dropin}.disabled ${dropin}
+	systemctl daemon-reload
+fi