MINOR: lua: Allow argument for actions

(http|tcp)-(request|response) action cannot take arguments from the
configuration file. Arguments are useful for executing the action with
a special context.

This patch adds the possibility of passing arguments to an action. It
runs exactly like sample fetches and other Lua wrappers.

Note that this patch implements a 'TODO'.

include/types/hlua.h

@@ -90,6 +90,7 @@ struct hlua_init_function {
 struct hlua_function {
 	char *name;
 	int function_ref;
+	int nargs;
 };
 
 /* This struct is used with the structs: