Use g_strdup instead of ignoring VIR_STRDUP's value

Replace all the occurrences of
  ignore_value(VIR_STRDUP(a, b));
with
  a = g_strdup(b);

Signed-off-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

tests/testutils.c

@@ -767,7 +767,7 @@ virTestLogContentAndReset(void)
         return NULL;
     ret = virBufferContentAndReset(&testLog.buf);
     if (!ret)
-        ignore_value(VIR_STRDUP(ret, ""));
+        ret = g_strdup("");
     return ret;
 }