ostbuild: Use .lastfetch file per branch
ostbuild: Use .lastfetch file per branch

This way we don't try to update gtk+ twice, once for gtk master and
once for gtk-2-22.

GNOME/ostree,sujitfulse/ostree,leandrosansilva/ostree,leandrosansilva/ostree,resin-io/ostree,leandrosansilva/ostree,gatispaeglis/ostree,gatispaeglis/ostree,GNOME/ostree,sujitfulse/ostree,resin-io/ostree,sujitfulse/ostree,sujitfulse/ostree,GNOME/ostree,gatispaeglis/ostree,resin-io/ostree,gatispaeglis/ostree,resin-io/ostree,GNOME/ostree,leandrosansilva/ostree,sujitfulse/ostree,gatispaeglis/ostree,resin-io/ostree,GNOME/ostree,leandrosansilva/ostree,gatispaeglis/ostree