Refactoring regarding LanItems.device and LanItems.interfacename.

interfacename used to be duplicate for device. So, it was removed and
replaced by device where needed.

Some code which filled device by oldfashioned name (id-<mac> or
id-<busid>) was removed as it is not supported format anymore.
Removed dead code and some Ycp -> Ruby artifacts
Refactoring LanUdevAuto#getDeviceName
Created rspec test for LanUdevAuto#getDeviceName
Added comments for LanUdevAuto#getDeviceName.