XFS support module

Hi!
Since XFS is an officially supported filesystem in the SUSE Enterprise Linux 12, I would like to introduce a little module for managing XFS filesystems. Apart from just creating filesystems, it can do much more, but everything. :-)

Some examples:

```
# salt '*' xfs.devices
helios:
    ----------
    /dev/sda2:
        ----------
        label:
            None
        partuuid:
            0006f5ee-02
        uuid:
            4f7d5544-3234-46ff-8420-4d704c00a476
    /dev/sda3:
        ----------
        label:
            Foobar
        mount_point:
            /foo
        options:
            - rw
            - relatime
            - attr2
            - inode64
            - sunit=64
            - swidth=384
            - noquota
        partuuid:
            0006f5ee-03
        uuid:
            a22204f1-1877-4915-b2f6-29989046e790
    /dev/sda5:
        ----------
        label:
            None
        mount_point:
            /
        options:
            - rw
            - relatime
            - attr2
            - inode64
            - noquota
        partuuid:
            0006f5ee-05
        uuid:
            0a7d355e-2ee0-4e73-be2e-cf88deeb87b7

# salt 'helios' xfs.dump /dev/sda5 /tmp/my-backup
helios:
    ----------
    Dump complete:
        158 seconds elapsed
    Media size:
        6254453024 bytes
    Session ID:
        f0efa5b4-cc1b-42ea-96b4-1421940aa056
    Session label:
        "XFS dump for "/dev/sda5" of 2014.11.01, 16:58"
    Status:
        SUCCESS
    Summary:
        stream 0 /tmp/my-backup OK (success)

# salt '*' xfs.prune_dump 2efce204-ea9a-420d-8a9c-e1a1cbb1f4c4
helios:
    ----------
    dev_path:
        helios:/dev/sda5
    label:
        XFS dump for "/dev/sda5" of 2014.11.01, 16:58
    mount_point:
        helios:/foo
    time_of_dump:
        Mon Nov  3 19:25:01 2014
    uuid:
        2efce204-ea9a-420d-8a9c-e1a1cbb1f4c4
```

Hope, you will like it. :-)