icingacli web serve: Fix "PHP Notice: Use of undefined constant ICINGA_LIBDIR"

application/clicommands/WebCommand.php

@@ -47,7 +47,7 @@ class WebCommand extends Command
             readlink('/proc/self/exe'),
             $socket,
             $basedir,
-            ICINGA_LIBDIR . '/Icinga/Application/webrouter.php'
+            Icinga::app()->getLibraryDir('/Icinga/Application/webrouter.php')
         );
 
         // TODO: Store webserver log, switch uid, log index.php includes, pid file

library/Icinga/Application/ApplicationBootstrap.php

@@ -275,6 +275,18 @@ abstract class ApplicationBootstrap
         return $this->getDirWithSubDir($this->configDir, $subDir);
     }
 
+    /**
+     * Get the Icinga library directory
+     *
+     * @param   string $subDir Optional sub directory to get
+     *
+     * @return  string
+     */
+    public function getLibraryDir($subDir = null)
+    {
+        return $this->getDirWithSubDir($this->libDir, $subDir);
+    }
+
     /**
      * Get the path to the bootstrapping directory
      *