GDBus tests: change progress noise from "if not quiet" to "if verbose"

It seems that even after Bug #711796, these can still interfere
with TAP testing:

PASS: gdbus-proxy-threads 1 /gdbus/proxy/vs-threads
tap-driver.sh: internal error getting exit status
tap-driver.sh: fatal: I/O or internal error

Let's shut them up unless --verbose is used (which would be appropriate
when running them interactively).

Similar symptoms have been seen in Debian:
https://buildd.debian.org/status/fetch.php?pkg=glib2.0&arch=mipsel&ver=2.39.91-1&stamp=1394394568
and in Guix:
https://lists.gnu.org/archive/html/bug-guix/2014-12/msg00002.html

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=725981
Reviewed-by: Philip Withnall <philip.withnall@collabora.co.uk>
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

gio/tests/gdbus-proxy-threads.c

@@ -71,7 +71,7 @@ run_proxy_thread (gpointer data)
       GError *error = NULL;
       GVariant *ret;
 
-      if (!g_test_quiet ())
+      if (g_test_verbose ())
         g_print (".");
 
       proxy = g_dbus_proxy_new_sync (connection,
@@ -232,7 +232,7 @@ test_proxy (void)
   /* TODO: should call session_bus_down() but that requires waiting
    * for all the oustanding method calls to complete...
    */
-  if (!g_test_quiet ())
+  if (g_test_verbose ())
     g_print ("\n");
 }