device_id: find camera by serial number

This brings back a feature from the old openni(1): Selecting a camera based
on its serial number.

The procedure is simple: When enumerating all available devices, briefly
open and query each one for its serial number. After that, compare the
given device_id with the available serial numbers and select the matching
camera (if available).

Tested with three Asus Xtion Pro Live cameras on Ubuntu 14.04 / Indigo / amd64.