Add coupled forecast-only tests for S2S and S2SW (#1895)

This PR:
- replaces the PR C48 S2S forecast-only test with a S2SW configuration
- adds a weekly C384 S2SWA forecast-only test.

The C384 S2SWA is a weekly test and will not be triggered/tested in this PR, but will
be tested on Friday.  See notes on Orion below in the testing section.

@JessicaMeixner-NOAA kindly provided the details in 
#1794 (comment)

ci/cases/pr/C48_S2S.yaml → ci/cases/pr/C48_S2SW.yaml

@@ -4,7 +4,7 @@ experiment:
 
 arguments:
   pslot: ${pslot}
-  app: S2S
+  app: S2SW
   resdet: 48
   comrot: ${RUNTESTS}/COMROT
   expdir: ${RUNTESTS}/EXPDIR

ci/cases/weekly/C384_S2SWA.yaml

@@ -0,0 +1,13 @@
+experiment:
+  type: gfs
+  mode: forecast-only
+
+arguments:
+  pslot: ${pslot}
+  app: S2SWA
+  resdet: 384
+  comrot: ${RUNTESTS}/COMROT
+  expdir: ${RUNTESTS}/EXPDIR
+  idate: 2016070100
+  edate: 2016070100
+  yaml: ${HOMEgfs_PR}/ci/platforms/gfs_defaults_ci-updates.yaml