Test: consistently use $(TEST_NETWORK_ALL_LOG_DIR) in Makefile.am

Part of 27295.

Makefile.am

@@ -128,7 +128,7 @@ test-network-all: need-chutney-path test-driver $(TESTING_TOR_BINARY) src/tools/
 		$(SHELL) $(top_srcdir)/test-driver --test-name $$f --log-file $(TEST_NETWORK_ALL_LOG_DIR)/$$f.log --trs-file $(TEST_NETWORK_ALL_LOG_DIR)/$$f.trs $(TEST_NETWORK_ALL_DRIVER_FLAGS) $(top_srcdir)/src/test/test-network.sh --flavor $$f $(TEST_NETWORK_FLAGS); \
 	done; \
 	echo "Log and result files are available in $(TEST_NETWORK_ALL_LOG_DIR)."; \
-	! grep -q FAIL test_network_log/*.trs
+	! grep -q FAIL $(TEST_NETWORK_ALL_LOG_DIR)/*.trs
 
 need-stem-path:
 	@if test ! -d "$$STEM_SOURCE_DIR"; then \