Add a getHostname to system
It is better to abstract how we retrieve the hostname than to access
it directly (see also getAppVersion).
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">
<head>
<title>500 Server Error</title>
</head>
<body><h1>500 Server Error</h1></body>
</html>