gtester: do not consider skipped tests as failures

This is happening since f591366eee, that
changed the way tests were skipped to use g_test_skip() instead of just
ignoring them. They are now reported to the log with G_TEST_RUN_SKIPPED
as result.

https://bugzilla.gnome.org/show_bug.cgi?id=790934

glib/gtestutils.h

@@ -354,6 +354,13 @@ typedef struct {
 GLIB_VAR const GTestConfig * const g_test_config_vars;
 
 /* internal logging API */
+typedef enum {
+  G_TEST_RUN_SUCCESS,
+  G_TEST_RUN_SKIPPED,
+  G_TEST_RUN_FAILURE,
+  G_TEST_RUN_INCOMPLETE
+} GTestResult;
+
 typedef enum {
   G_TEST_LOG_NONE,
   G_TEST_LOG_ERROR,             /* s:msg */