title: Icinga2 check_mem plugin doesn't accept parameters
body: <p>​Hello,</p>
  
  <p>I've created a custom command in Icinga 2 using this plugin:</p>
  
  <p><a href="https://github.com/justintime/nagios-plugins/blob/master/check_mem/check_mem.pl" rel="nofollow">https://github.com/justintime/nagios-plugins/blob/master/check_mem/check_mem.pl</a>​</p>
  
  <h1>check_command</h1>
  
  <pre><code>object CheckCommand "memory" {
    import "plugin-check-command"
    command = [ PluginDir + "/check_mem" ]
  
    arguments = {
      "-w" = {
       required = true 
       value = "$mem_warning$"
      }
  
      "-c" = {
       required = true
       value = "$mem_critical$"
      }
      "-u" = {
       required = true
       value = "$mem_used$"
      }
  
      "-C" = "$mem_cache$"
    }
  
    vars.mem_used = true
    vars.mem_cache = true
    vars.mem_warning = 85
    vars.mem_critical = 95
  </code></pre>
  
  <p>}</p>
  
  <h1>service</h1>
  
  <pre><code>apply Service "Memory" {
    import "generic-service"
    check_command = "memory"
    assign where host.address
  }
  </code></pre>
  
  <p>However the plugin cannot check the memory and gives the following output in Icinga Web 2 interface:</p>
  
  <h1>​Plugin Output</h1>
  
  <p>*** You must define WARN and CRITICAL levels!
  \ncheck_​mem.​pl v1.​0 - Nagios Plugin\n\nusage:​\n check_​mem.​pl -\ncheck_​mem.​pl comes with absolutely NO WARRANTY either implied or explicit\nThis program is licensed under the terms of the\nMIT License (check source code for details)</p>
  
  <p>Could you please help, what is wrong with this check?</p>