Modify forecast script to get correct background.

[christinaholtNOAA]

The existing script in RRFS_dev1 contains logic about whether the run should be a cold start or a cycled forecast. It also handles:

• Where to run the task, subdirectories for fcst_fv3lam_spinup, fcst_fv3lam_ensinit, or fcst_fv3lam
• Decide where to get data for either cold start or warm start.
• Convert netcdf4 to netcdf3 -- this has a dependency on ncks, which may come from the nco module.

It also has some logic to handle running ensemble members. This may or may not already be handled in the develop branch.

[christinaholtNOAA]

Suspending development of RRFS GSI capabilities.