volumes: set hostPath based on volume id

this is required for the file browser to work which does operations
based on the id

fixes #789

src/scripts/rmmount.sh

@@ -23,4 +23,5 @@ mount_filename=$(systemd-escape -p --suffix=mount "$where")
 
 systemctl stop "${mount_filename}" || true
 rm -f "/etc/systemd/system/${mount_filename}"
+rmdir "${where}" || true
 systemctl daemon-reload