Run METplus serially and correct the name of prod tasks (#2804)

Adds 2 hot fixes:

- METplus v9.1.3 has a bug in it that sometimes attempts to create
multiple copies of the same directory when running in parallel, causing
a Python error and downstream problems. This PR makes METplus run in
serial mode, preventing such issues.
- Corrects the name of the atmos_prod, ocean_prod, and ice_prod tasks in
workflow/rocoto/tasks.py (was accidentally changed to e.g. atmosprod)

parm/config/gfs/config.resources

@@ -889,8 +889,8 @@ case ${step} in
     threads_per_task=1
     walltime_gdas="03:00:00"
     walltime_gfs="06:00:00"
-    ntasks=4
-    tasks_per_node=4
+    ntasks=1
+    tasks_per_node=1
     export memory="80G"
     ;;
 

workflow/rocoto/tasks.py

@@ -24,7 +24,7 @@ class Tasks:
                    'prepsnowobs', 'snowanl',
                    'fcst',
                    'atmanlupp', 'atmanlprod', 'atmupp', 'goesupp',
-                   'atmosprod', 'oceanprod', 'iceprod',
+                   'atmos_prod', 'ocean_prod', 'ice_prod',
                    'verfozn', 'verfrad', 'vminmon',
                    'metp',
                    'tracker', 'genesis', 'genesis_fsu',