Fix hostname regex check

Set a minimal length so that the check doesn't fail

bin/xen-create-image

@@ -1548,7 +1548,7 @@ sub checkOption
             message => "must be valid IPv4.\n",
         },
         hostname => {
-            check   => qr/^[a-z0-9][a-z0-9.-]{254}$/i,
+            check   => qr/^[a-z0-9][a-z0-9.-]{0,254}$/i,
             message => "must be a valid hostname.\n",
         },
         supportedFs => {