Another weird edge case with date stamps in rpointer files

@kristenkrumhardt created a new CESM case, set `RUN_TYPE=branch` and also set up `RUN_REFCASE` and `RUN_REFDATE`. After she built the model and the submitted job started running, the coupler aborted immediately with

```
read rpointer file = rpointer.cpl
(esm_time_mod.F90:esm_time_clockInit) ERROR rpointer file rpointer.cpl not foun
d
```

We traced the issue to `DRV_RESTART_POINTER` being `rpointer.cpl` rather than `rpointer.cpl.YYYY-MM-DD-SSSSS`, but should there be a mechanism to tell CIME to include `REF_DATE` when constructing `DRV_RESTART_POINTER`? Maybe the default should be to include it when `CONTINUE_RUN=FALSE`, but there can be a mechanism to say "no, just use `rpointer.cpl` instead?

We think this maybe leads to unexpected inconsistencies in `hybrid` runs, because similar steps but using `RUN_TYPE=hybrid` does not abort. Perhaps the coupler just initializes itself as a startup if `DRV_RESTART_POINTER` is not found in a hybrid run? Some of the components initialized from restart files, so it's a little unclear what actually happened in the hybrid case...

Start with esm_time_mod.F90:esm_time_clockInit and trace how CIME constructs DRV_RESTART_POINTER for RUN_TYPE=branch, including RUN_REFDATE and CONTINUE_RUN. Compare the resulting rpointer.cpl handling with a RUN_TYPE=hybrid case; done means branch runs find the intended dated pointer file without regressing valid hybrid or startup behavior.

Written by the indexing model from the issue text.