Make job_start_data() multi partition aware on REQUEST_JOB_WILL_RUN.

Previously the function was only testing against the first partition in
the job_record. Now it detects if the job request is multi partition and
if so then loops through all of them until the job will run in any or
until the end of the list, returning the error code from the last one if
the job won't run in any partition.

Bug 5185