ds-identify cannot identify disk-based resources on FreeBSD

[Mina Galić]

Following https://github.com/canonical/cloud-init/pull/617
i tried to replicate this on my laptop.

In a FreeBSD 12, there is no `blkid`. That means that the NoCloud seed image, which was provided as iso9660 formatted disk with the label 'cidata' was not found.
The equivalent tool on FreeBSD to find disks and their labels would be `geom`:

```
meena@fbsd12-1 /u/h/meena> geom label status -a
          Name Status Components
  gpt/gptboot0 N/A vtbd1p1
     gpt/swap0 N/A vtbd1p2
iso9660/cidata N/A vtbd2
```

and here, in -s for script-friendly output:

```
meena@fbsd12-1 /u/h/meena> geom label status -as
  gpt/gptboot0 N/A vtbd1p1
     gpt/swap0 N/A vtbd1p2
iso9660/cidata N/A vtbd2
```

where we have type/label followed by status and and then device name (a partition or slice)

We should change read_fs_info() to call a `blkid` or `geom` parser function based on which OS we're on.

[Paride Legovini (paride)]

PR fixing this:

https://github.com/canonical/cloud-init/pull/625

Thanks Mina!

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3799