purge: fix purge of lvm devices

purge: fix purge of lvm devices

using `shell` module seems to be the only way to make this task working
on rhel based distribution AND debian based distributions.

on ubuntu, using `command` ansible module fails like following
(not due to `sudo` usage or not):
```
ok: [osd1] => changed=false
  cmd: command -v ceph-volume
  failed_when_result: false
  msg: '[Errno 2] No such file or directory: ''command'': ''command'''
  rc: 2
```

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1653307
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>