Persist zwave_js device config files (#2038)

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

zwave_js/rootfs/etc/cont-init.d/structure.sh

@@ -3,3 +3,4 @@
 # Setup folder structure
 # ==============================================================================
 mkdir -p /data/cache
+mkdir -p /data/db

zwave_js/rootfs/etc/services.d/zwave_js/run

@@ -12,5 +12,8 @@ fi
 # Send out discovery information to Home Assistant
 ./discovery &
 
-# Run daemon
+# Set external config directory
+export ZWAVEJS_EXTERNAL_CONFIG=/data/db
+
+# Run daemon, passing external config directory in as environment variable
 exec zwave-server ${SERIAL_DEVICE} --config /etc/zwave_config.json