Icingacli should return UNKNOWN code, showUsage() also should return non-zero

library/Icinga/Application/Cli.php

@@ -151,8 +151,8 @@ class Cli extends ApplicationBootstrap
         if ($this->showBenchmark) {
             Benchmark::dump();
         }
-        if (false === $result) {
-            exit(1);
+        if ($result === false) {
+            exit(3);
         }
     }
 

library/Icinga/Cli/Command.php

@@ -197,6 +197,7 @@ abstract class Command
             $this->commandName,
             $action
         );
+        return false;
     }
 
     public function init()