cc_disk_setup always overwrites filesystem on raw disk

This bug was originally filed in Launchpad as [LP: #1943156](https://bugs.launchpad.net/cloud-init/+bug/1943156)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2021-09-09T15:21:00.623940+00:00

date_fix_committed = None

date_fix_released = None

id = 1943156

importance = medium

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1943156

milestone = None

owner = optimum-reflex

owner_name = xstaticxgpx

private = False

status = triaged

submitter = optimum-reflex

submitter_name = xstaticxgpx

tags = []

duplicates = []

_Launchpad user **xstaticxgpx(optimum-reflex)** wrote on 2021-09-09T15:21:00.623940+00:00_

See https://github.com/canonical/cloud-init/blob/758acf976f2cb67a85411467fa5fca2ea17a2283/cloudinit/config/cc_disk_setup.py#L1005-L1009

```
# File systems that support the -F flag
if overwrite or device_type(device) == "disk":
force_flag = lookup_force_flag(fs_type)
if force_flag:
fs_cmd.append(force_flag)
```

Even with `overwrite: false` when using a raw disk device (ie. /dev/sdb) the filesystem will always be overwritten. This seems unintended, as it's definitely not clarified in the documentation.

I think at the very least the documentation should be clarified that raw disk devices will ALWAYS be overwritten by default.

We ended up overwriting our `cmd` value to prevent the force flag from being added...

```
- label: DATA
filesystem: xfs
device: /dev/sdb
cmd: '/usr/sbin/mkfs.xfs %(device)s -L %(label)s'

```