update user password fails when machine does not have openssh installed

This bug was originally filed in Launchpad as [LP: #1901761](https://bugs.launchpad.net/cloud-init/+bug/1901761)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2020-10-27T20:15:44.000418+00:00

date_fix_committed = None

date_fix_released = None

id = 1901761

importance = low

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1901761

milestone = None

owner = lamoura

owner_name = Lucas Albuquerque Medeiros de Moura

private = False

status = triaged

submitter = lamoura

submitter_name = Lucas Albuquerque Medeiros de Moura

tags = []

duplicates = []

_Launchpad user **Lucas Albuquerque Medeiros de Moura(lamoura)** wrote on 2020-10-27T20:15:44.000418+00:00_

When creating a machine with the following userdata:

```
#cloud-config
chpasswd:
list: |
ubuntu:passw0rd
ssh_pwauth: True
```

cloud-init will fails if the machine does not have openssh installed on it. That happens because pasasword module will try to run the following command:

```
service ssh restart
```

Which will fail if the machine does not have openssh installed.

How to reproduce:

Just launch an lxd vm with the provided userdata using the following image as base: `images:ubuntu/16.04/cloud`