itest: fix itest logs upload

When one of the itest tranches fails, because we are running tests in
parallel, other tranches will still be running, which caused 7z to fail
at zipping the logs because race reads. This commit fixes it by making
sure we are waiting other tranches to finish before moving to zipping
and uploading the logs.

Makefile

@@ -174,7 +174,7 @@ itest-race: build-itest-race itest-only
 itest-parallel: build-itest db-instance
 	@$(call print, "Running tests")
 	rm -rf itest/*.log itest/.logs-*; date
-	EXEC_SUFFIX=$(EXEC_SUFFIX) echo "$$(seq 0 $$(expr $(ITEST_PARALLELISM) - 1))" | xargs -P $(ITEST_PARALLELISM) -n 1 -I {} scripts/itest_part.sh {} $(NUM_ITEST_TRANCHES) $(TEST_FLAGS) $(ITEST_FLAGS)
+	EXEC_SUFFIX=$(EXEC_SUFFIX) scripts/itest_parallel.sh $(ITEST_PARALLELISM) $(NUM_ITEST_TRANCHES) $(TEST_FLAGS) $(ITEST_FLAGS)
 
 itest-clean:
 	@$(call print, "Cleaning old itest processes")