Fix IC linking in setup_expt.py (NOAA-EMC#1885)

This fixes a bug in IC linking within setup_expt.py by correcting the date string
based on experiment start type -- warm starts should look at `rdate` (-6 hours)
and cold starts should look at `idate` (current cycle).

Fixes NOAA-EMC#1783

workflow/setup_expt.py

@@ -71,7 +71,15 @@ def fill_COMROT_cycled(host, inputs):
     rdatestr = datetime_to_YMDH(inputs.idate - to_timedelta('T06H'))
     idatestr = datetime_to_YMDH(inputs.idate)
 
-    if os.path.isdir(os.path.join(inputs.icsdir, f'{inputs.cdump}.{rdatestr[:8]}', rdatestr[8:], 'model_data', 'atmos')):
+    # Test if we are using the new COM structure or the old flat one for ICs
+    if inputs.start in ['warm']:
+        pathstr = os.path.join(inputs.icsdir, f'{inputs.cdump}.{rdatestr[:8]}',
+                               rdatestr[8:], 'model_data', 'atmos')
+    else:
+        pathstr = os.path.join(inputs.icsdir, f'{inputs.cdump}.{idatestr[:8]}',
+                               idatestr[8:], 'model_data', 'atmos')
+
+    if os.path.isdir(pathstr):
         flat_structure = False
     else:
         flat_structure = True