[test] Adapted set_metadata() test to API changes.
[test] Adapted set_metadata() test to API changes.

MikePetullo/grilo-plugins,MathieuDuponchelle/grilo-plugins,GNOME/grilo-plugins,grilofw/grilo-plugins,grilofw/grilo-plugins,vrutkovs/grilo-plugins,MikePetullo/grilo-plugins,kyoushuu/grilo-plugins,MathieuDuponchelle/grilo-plugins,vrutkovs/grilo-plugins,vrutkovs/grilo-plugins,MathieuDuponchelle/grilo-plugins,kyoushuu/grilo-plugins,GNOME/grilo-plugins,jasuarez/grilo-plugins,jasuarez/grilo-plugins,vrutkovs/grilo-plugins,MathieuDuponchelle/grilo-plugins,kyoushuu/grilo-plugins,MikePetullo/grilo-plugins