core: Don't use expired cache of description doc
core: Don't use expired cache of description doc

If the template device description was modified after cached description
was modified/created, use the template device description. Without this
change, user had to manually remove the cached description documents each
time we modified the templates.

GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,Pelagicore/Media-Manager-Rygel-patched,GNOME/rygel,jku/rygel,Pelagicore/Media-Manager-Rygel-patched,jku/rygel,GNOME/rygel,luisbg/rygel,Tarnyko/rygel,Tarnyko/rygel