Use format field in file as lvcnrcheck default

Falling back to format level 1 if the field is missing in the file to be
checked.

bin/lvcnrcheck

@@ -35,7 +35,11 @@ parser.add_argument(
     help='use coloured output', action='store_true')
 parser.add_argument(
     '-f', '--format',
-    help='format level to use', type=int, choices=[1, 2, 3], default=1)
+    help=(
+        "format level to use, if not provided the format level specified in "
+        "file will be used, if the format field is missing from file format "
+        "level 1 will be used"),
+    type=int, choices=[1, 2, 3])
 args = parser.parse_args()
 
 # Define output syntax for a single field report
@@ -92,7 +96,10 @@ if __name__ == '__main__':
 
         print('')
 
-    if args.format > 1:
+    # Determine format level to check
+    fmt = args.format or sim.att('Format') or 1
+
+    if fmt > 1:
         # Format 2
         print('# Format 2\n')
 
@@ -101,7 +108,7 @@ if __name__ == '__main__':
 
         print('')
 
-    if args.format > 2:
+    if fmt > 2:
         # Format 3
         print('# Format 3\n')