Modify tracking one step behind model using suite.rc

[jonseddon]

To run the tracking when the netCDF files are known to be available there is currently some logic in suite.rc:

postproc[+{{EXPT_RESUB}}] => tracking

this is bad because log files have been deleted by then and for other reasons.

It would be better to have logic in the Python that looks at the model resubmission period and the stream reinitialisation period that knows what files have become available and need to be tracked.

An approach similar to postproc that creates .arch files (perhaps .track) to know which files have been tracked could be used.

[jonseddon]

This may be best implemented once #15 has been completed.