The systemd shutdown script gets called after /snap/fwupd/* gets
unmounted meaning it can't be used to do the activation.
Explicitly check that the symlink for /snap/fwupd/current is mounted
when calling the script.
This is intended for devices that it is not safe to immediately activate
the firmware. It may be called at a more convenient time instead.
Both fwupdmgr and fwupdtool support the feature.
- if called at runtime with fwupdmgr it uses the daemon
- during shutdown fwupdtool uses the pending.db to perform this feature.
