Fixed error messages in installer.

Author: tbrehm

install/lib/installer_base.lib.php

@@ -664,10 +664,10 @@ public function install_ispconfig()
 
 		//* Create a ISPConfig user and group
 		$command = 'groupadd ispconfig';
-		caselog($command.' &> /dev/null', __FILE__, __LINE__, "EXECUTED: $command", "Failed to execute the command $command");
+		caselog($command.' &> /dev/null 2> /dev/null', __FILE__, __LINE__, "EXECUTED: $command", "Failed to execute the command $command");
 
 		$command = "useradd -g ispconfig -d $install_dir ispconfig";
-		caselog($command.' &> /dev/null', __FILE__, __LINE__, "EXECUTED: $command", "Failed to execute the command $command");
+		caselog($command.' &> /dev/null 2> /dev/null', __FILE__, __LINE__, "EXECUTED: $command", "Failed to execute the command $command");
 
 		//* copy the ISPConfig interface part
 		$command = "cp -rf ../interface $install_dir";