Fix ocnpost detection for gfs free-forecast

The task list for the free-forecast was checking against a list of
apps that did not include S2SA to determine whether ocnpost is
included. That check is now changed to check on do_ocean rather than
looking at the app directly.

Refs: #1593

workflow/applications/gfs_forecast_only.py

@@ -76,7 +76,7 @@ def get_task_names(self):
         if self.do_atm:
             tasks += ['post']
 
-        if self.model_app in ['S2S', 'S2SW', 'S2SWA', 'NG-GODAS']:
+        if self.do_ocean:
             tasks += ['ocnpost']
 
         if self.do_atm: