Add a script to process backlogs created while perf dashboard was in the maintenance...

Add a script to process backlogs created while perf dashboard was in the maintenance mode
https://bugs.webkit.org/show_bug.cgi?id=154140

Reviewed by Chris Dumez.

Added a script to process the backlog JSONs created while the perf dashboard was put in the maintenance mode.
It re-submits each JSON file to the perf dashboard using the same server config file used by syncing scripts.

* public/include/report-processor.php:
(TestRunsGenerator::test_value_list_to_values_by_iterations): Fixed a bug in the error message code. It was
referencing an undeclared variable.
* tools/process-maintenance-backlog.py: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@196459 268f45cc-cd09-0410-ab3c-d52691b4dbfc