tests: replace most g_print() with g_printerr()

I searched all files that mention g_test_run, and replaced most
g_print() calls. This avoids interfering with TAP. Exceptions:

* gio/tests/network-monitor: a manual mode that is run by
  "./network-monitor --watch" is unaffected
* glib/gtester.c: not a test
* glib/gtestutils.c: not a test
* glib/tests/logging.c: specifically exercising g_print()
* glib/tests/markup-parse.c: a manual mode that is run by
  "./markup-parse --cdata-as-text" is unaffected
* glib/tests/testing.c: specifically exercising capture of stdout
  in subprocesses
* glib/tests/utils.c: captures a subprocess's stdout
* glib/tests/testglib.c: exercises an assertion failure in g_print()

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=725981
Reviewed-by: Colin Walters <walters@verbum.org>
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

gio/tests/gdbus-proxy-threads.c

@@ -72,7 +72,7 @@ run_proxy_thread (gpointer data)
       GVariant *ret;
 
       if (g_test_verbose ())
-        g_print (".");
+        g_printerr (".");
 
       proxy = g_dbus_proxy_new_sync (connection,
                                      G_DBUS_PROXY_FLAGS_DO_NOT_AUTO_START |
@@ -233,7 +233,7 @@ test_proxy (void)
    * for all the oustanding method calls to complete...
    */
   if (g_test_verbose ())
-    g_print ("\n");
+    g_printerr ("\n");
 }
 
 int