MXS-1300: Return a rejected promise for unknown commands

When an unknow command is executed, the core should return a rejected
promise.

maxctrl/lib/link.js

@@ -43,7 +43,9 @@ exports.builder = function(yargs) {
         })
         .usage('Usage: link <command>')
         .help()
-        .command('*', 'the default command', {}, () => {
-            logger.log('Unknown command. See output of `help link` for a list of commands.')
+        .command('*', 'the default command', {}, function(argv) {
+            maxctrl(argv, function(host) {
+                return error('Unknown command. See output of `help link` for a list of commands.')
+            })
         })
 }