qapi: allow a 'gen' key to suppress code generation

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

scripts/qapi-commands.py

@@ -405,6 +405,7 @@ except os.error, e:
 
 exprs = parse_schema(sys.stdin)
 commands = filter(lambda expr: expr.has_key('command'), exprs)
+commands = filter(lambda expr: not expr.has_key('gen'), commands)
 
 if dispatch_type == "sync":
     fdecl = open(h_file, 'w')

scripts/qapi-types.py

@@ -238,6 +238,7 @@ fdecl.write(mcgen('''
                   guard=guardname(h_file)))
 
 exprs = parse_schema(sys.stdin)
+exprs = filter(lambda expr: not expr.has_key('gen'), exprs)
 
 for expr in exprs:
     ret = "\n"