ec2-cloudinit service fails after reboot with "reboot-strategy: off"

Steps to reproduce:

Boot a CoreOS machine with the following cloud-config:

```
#cloud-config
coreos:
    update:
        reboot-strategy: off
```

On first boot, everything is fine.  journalctl reports:

```
systemd[1]: Starting Cloudinit from EC2-style metadata...
coreos-cloudinit[3434]: 2014/05/21 17:27:14 Fetching user-data from datasource of type "metadata-service"
coreos-cloudinit[3434]: 2014/05/21 17:27:14 Parsing user-data as cloud-config
coreos-cloudinit[3434]: 2014/05/21 17:27:14 Wrote locksmith config file to filesystem
systemd[1]: Started Cloudinit from EC2-style metadata.
```

Reboot the system.  Now we see:

```
-- Reboot --
systemd[1]: Starting Cloudinit from EC2-style metadata...
coreos-cloudinit[3639]: 2014/05/21 17:28:51 Fetching user-data from datasource of type "metadata-service"
coreos-cloudinit[3639]: 2014/05/21 17:28:51 Parsing user-data as cloud-config
coreos-cloudinit[3639]: 2014/05/21 17:28:51 Failed to write locksmith config to filesystem: symlink /dev/null /etc/systemd
systemd[1]: ec2-cloudinit.service: main process exited, code=exited, status=1/FAILURE
systemd[1]: Failed to start Cloudinit from EC2-style metadata.
systemd[1]: Unit ec2-cloudinit.service entered failed state.

```

FWIW, the version I'm running:

```
$ cat /etc/lsb-release
DISTRIB_ID=CoreOS
DISTRIB_RELEASE=317.0.0
DISTRIB_CODENAME="Let the tiger loose!"
DISTRIB_DESCRIPTION="CoreOS 317.0.0"
```