process_tracker_python-81 Extract finders should return ExtractTracker objects, not Extracts

🐛  Config file had wrong parameter input - also for mysql

Documentation and the config file didn't match.  Have modified config file
to now match the documentation.

Closes #81

Author: Alex Meadows

configs/mysql_config.ini

@@ -1,6 +1,6 @@
 [DEFAULT]
 log_level = ERROR
-max_sequential_failures = 5
+max_concurrent_failures = 5
 data_store_type = mysql
 data_store_username = pt_admin
 data_store_password = Testing1!