Ensure that kube-apiserver starts after etcd

If etcd is running on the same system as kube-apiserver and is
being started as part of the same series of services (such as with a
custom systemd target), we need to ensure that it orders later in
startup than etcd or it will fail to find the local service.

Note: this does not attempt to start etcd on the local system if it
is not already part of the transaction, so it will have no effect
if someone calls `systemctl start kube-apiserver.service` directly.

contrib/init/systemd/kube-apiserver.service

@@ -2,6 +2,8 @@
 Description=Kubernetes API Server
 Documentation=https://github.com/GoogleCloudPlatform/kubernetes
 
+After=etcd.service
+
 [Service]
 EnvironmentFile=-/etc/kubernetes/config
 EnvironmentFile=-/etc/kubernetes/apiserver