Doing Install from file… and navigating to /home/clevouser/.config/blender/2.78/scripts/addons/system_cycles_material_texture_node.py (this script) gives me error “Source file is in the addon search path /home/clevouser/.config/blender/2.78/scripts/addons/”. Script not added to blender.
If it’s a single .py file addon you shouldn’t have to “Install from file”. It should just show up under list of addons. If it doesn’t maybe it needs updated for latest blender. If your doing a .zip file(multiple file addon) and “Install from file”. I always place those in the the python > lib folder or you will get a error if you place in addons folder.
strikes me that it’s already installed. Have you had a look to check it’s not already installed addons but simply not enabled?