Allow dynamic configuration for devices and filesystems

Currently our module is limited to `sdb`, `sdc` and `sdd` volume with `swift::storage::xfs` class.
This change aims to give the user total freedom of the name and the filesystem.

Hence the following become possible

```puppet
swift::storage::loopback {'loop0' : }
```
or

```puppet
swift::storage::disk {'sda' : }
```