purge: actually remove of /var/lib/ceph/*

purge: actually remove of /var/lib/ceph/*

38dc20e74b89c1833d45f677f405fe758fd10c04 introduced a bug in the purge
playbooks because using `*` in `command` module doesn't work.

`/var/lib/ceph/*` files are not purged it means there is a leftover.

When trying to redeploy a cluster, it failed because monitor daemon was
detecting existing keyring, therefore, it assumed a cluster already
existed.

Typical error (from container output):

```
Sep 26 13:18:16 mon0 docker[31316]: 2018-09-26 13:18:16  /entrypoint.sh: Existing mon, trying to rejoin cluster...
Sep 26 13:18:16 mon0 docker[31316]: 2018-09-26 13:18:16.9323937f15b0d74700 -1 auth: unable to find a keyring on /etc/ceph/test.client.admin.keyring,/etc/ceph/test.keyring,/etc/ceph/keyring,/etc/ceph/keyring.bin,:(2) No such file or directory
Sep 26 13:18:23 mon0 docker[31316]: 2018-09-26 13:18:23  /entrypoint.sh:
SUCCESS
```

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1633563
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>