The JobSchedulerExistsFile job should use the SCHEDULER_FILE_PATH parameter if available

Current Situation
The checkExistFile job does not use the SCHEDULER_FILE_PATH parameter if used in a job chain with a file order source.

Desired Behavior

• If the parameters file_spec, file are empty and the job is used in a job chain with a file order source then the value of the SCHEDULER_FILE_PATH parameter should be used as a default value for the file and file_spec parameters.