mtp: use "storage-description (hex-storage-id)" for storage name instead of just "storage-description"

Storage description by itself is not unique, thus using it for storage name on its own causes problems when multiple storages with the same description are present (i.e., only one is listed and even that one incorrectly referenced in some situations - [Bug 733465]). The proposed storage name format is used both as name and display name.

On my TF701 with two SD cards, Nautilus now properly lists: "Internal storage (10001)", "SD card (20001)" and "SD card (30001)", and the corresponding URIs are:
mtp://[usb:001,005]/Internal storage (10001)
mtp://[usb:001,005]/SD card (20001)
mtp://[usb:001,005]/SD card (30001)

Signed-off-by: Rok Mandeljc <rok.mandeljc@gmail.com>
mtp: use "storage-description (hex-storage-id)" storage name format only when necessary

This patch implements on-demand post-fixing of storage description with ID for storage name, i.e., only in cases, when description itself is not unique.

Signed-off-by: Rok Mandeljc <rok.mandeljc@gmail.com>