Use uppercased 'u' in brand filename for OpenSUSE >= 13.1. Fix #57.

Reuse the existing detector. Just provide a new value for the 'brand_file'
parameter.
Add testcase for OpenSUSE >= 13.1 detection.
Merge pull request #68 from gavanderhoorn/issue57_suse13_os_detect

Add detection case for OpenSUSE >= 13.1 (changed case of brand_file)