In currently, swift::storage::xfs will mount device by its file path,
like /dev/sda1. But the device file path will change when the computer
reboots. This will lead Swift services fails to boot.
This patch introduces $device_type param to support mount disk by UUIDs.
By default, it will set to 'path' to keep compatiable.
Change-Id: I1782c0b18a27203e90d27473d94fa16968c3f913