Use NETBIOS name for non-domain hosts instead of hostname

Fixes #49

Author: LordHepipud

lib/core/icingaagent/getters/Get-IcingaNetbiosName.psm1

@@ -0,0 +1,6 @@
+function Get-IcingaNetbiosName()
+{
+    $ComputerData = Get-WmiObject Win32_ComputerSystem;
+
+    return $ComputerData.Name;
+}

lib/core/tools/Get-IcingaUserSID.psm1

@@ -12,7 +12,7 @@ function Get-IcingaUserSID()
         $Domain   = $TmpArray[0];
         $Username = $TmpArray[1];
     } else {
-        $Domain   = Get-IcingaHostname;
+        $Domain   = Get-IcingaNetbiosName;
         $Username = $User;
     }