Newer GLib's want unique test paths, and thus moan at dupes.
(Seen on Fedora 23 which has glib 2.46)

Uniquify the paths.
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>