Description of problem:
atomic-openshift-node service failed to start while enabling node and docker system container. The root cause is that the node unit file was fetched from node image which hard coded to configure docker as the dependence. Instead it should require container-engine while enabling docker system container.

Version-Release number of the following components:
openshift-ansible-3.7.0-0.128.0.git.0.89dcad2.el7.noarch.rpm

How reproducible:
always

Steps to Reproduce:
1. cat inventory_file:
<--snip-->
containerized=true
openshift_use_system_containers=true
system_images_registry=registry.xxx.openshift.com
openshift_docker_use_system_container=true
<--snip-->
2.
3.

Actual results:
# systemctl cat atomic-openshift-node
# /etc/systemd/system/atomic-openshift-node.service
[Unit]
After=docker.service
After=openvswitch.service
Wants=docker.service
After=atomic-openshift-node-dep.service
After=atomic-openshift-master.service
Requires=dnsmasq.service
After=dnsmasq.service

[Service]
Type=notify
EnvironmentFile=/etc/sysconfig/atomic-openshift-node
EnvironmentFile=/etc/sysconfig/atomic-openshift-node-dep

ExecStartPre=/usr/bin/cp /etc/origin/node/node-dnsmasq.conf /etc/dnsmasq.d/
ExecStartPre=/usr/bin/dbus-send --system --dest=uk.org.thekelleys.dnsmasq /uk/org/thekelleys/dnsmasq uk.org.thekelleys.SetDomainServers array:string:/in-addr.arpa/127.0.0.1,
ExecStopPost=/usr/bin/rm /etc/dnsmasq.d/node-dnsmasq.conf
ExecStopPost=/usr/bin/dbus-send --system --dest=uk.org.thekelleys.dnsmasq /uk/org/thekelleys/dnsmasq uk.org.thekelleys.SetDomainServers array:string:

ExecStartPre=/bin/bash -c 'export -p > /run/atomic-openshift-node-env'
ExecStart=/bin/runc --systemd-cgroup run 'atomic-openshift-node'
ExecStop=/bin/runc --systemd-cgroup kill 'atomic-openshift-node'
SyslogIdentifier=atomic-openshift-node
Restart=always
RestartSec=5s
WorkingDirectory=/var/lib/containers/atomic/atomic-openshift-node.0
RuntimeDirectory=atomic-openshift-node

[Install]
WantedBy=docker.service

Expected results:

Additional info:
node system container maybe work with rpm docker service or container-engine service, we need take the two situations into consideration when fxing this bug