Prefer /usr/share/metainfo as default path for metainfo files
Prefer /usr/share/metainfo as default path for metainfo files

follow-up from commit 9df56f2

ximion/appstream-glib,ximion/appstream-glib,ximion/appstream-glib,hughsie/appstream-glib,hughsie/appstream-glib,hughsie/appstream-glib