__netbox*: added systemd socket support

The Gunicorn type now supports systemd sockets only. With uWSGI, you can
choose between it and the native sockets based on the parameters chosen.
This is done because it could not be implemented to have multiple
protocols with the systemd sockets (so you may choose).

The systemd socket unit file is generally available, so both types use
the same script to generate the socket unit file.

type/__netbox/files/netbox.socket.sh

@@ -0,0 +1,33 @@
+#!/bin/sh -e
+# __netbox/files/netbox.socket.sh
+
+# This is shared between all WSGI-server types.
+
+# Arguments:
+#  1: File which list all sockets to listen on (sepearated by \n)
+
+if [ $# -ne 1 ]; then
+    printf "netbox.socket.sh: argument \$1 missing or too much given!\n" >&2
+    exit 1
+fi
+
+
+cat << UNIT
+[Unit]
+Description=Socket for NetBox via $TYPE
+
+[Socket]
+UNIT
+
+# read all sockets to listen to
+while read line; do
+    printf "ListenStream=%s\n" "$line"
+done < "$1"
+
+cat << UNIT
+SocketUser=netbox
+SocketGroup=www-data
+
+[Install]
+WantedBy=sockets.target
+UNIT