Added skip-pnl to cesm's template.case.run

Added the new skip-preview-namelist option to the cesm version of
template.case.run.

Test suite: scripts_regression_tests.py
Test baseline:
Test namelist changes:
Test status: bit for bit

Fixes #1276

User interface changes?: Adds --skip-preview-namelist

Code review: @jgfouca, @rljacob

config/cesm/machines/template.case.run

@@ -52,12 +52,18 @@ formatter_class=argparse.ArgumentDefaultsHelpFormatter
     parser.add_argument("--caseroot",
                         help="Case directory to build")
 
+    parser.add_argument("--skip-preview-namelist", action="store_true",
+                        help="Skip calling preview-namelist during case.run")
+
     args = CIME.utils.parse_args_and_handle_standard_logging_options(args, parser)
 
     if args.caseroot is not None:
         os.chdir(args.caseroot)
 
-    return args.caseroot
+    if args.skip_preview_namelist is None:
+      args.skip_preview_namelist = False
+
+    return args.caseroot, args.skip_preview_namelist
 
 ###############################################################################
 def _main_func(description):
@@ -66,9 +72,9 @@ def _main_func(description):
         test_results = doctest.testmod(verbose=True)
         sys.exit(1 if test_results.failed > 0 else 0)
 
-    caseroot = parse_command_line(sys.argv, description)
+    caseroot, skip_pnl = parse_command_line(sys.argv, description)
     with Case(caseroot, read_only=False) as case:
-        success = case_run(case)
+        success = case_run(case, skip_pnl=skip_pnl)
 
     sys.exit(0 if success else 1)