Over the months the original meaning of ALLOW_OFFLINE and ALLOW_ONLINE have be
lost, and there is now a confusing mixture of uses in the source tree. With this
commit we make it clear the UPDATABLE flag is used to specify when the device is
updatable (e.g. from the desktop live session, or from the systemd offline
updates mode, or both) and the NEEDS_REBOOT flag lets us know when the update
is actually going to be done.
For instance, a UEFI UpdateCapsule can be *scheduled* from either the desktop
or from the update mode (but the latter would be a bit weird), but does require
a reboot. Some devices might only be updatable outside the live session, for
instance a hard drive update or a GPU update -- there's just too much going on
with a live session and we want to tightly control what's running during the
firmware flash.
This also means we don't have to "retry" the update when scheduling an update
that really can be scheduled whenever, but just requires a reboot to apply.
This functionality is required so that AppStream metadata can check the fwupd
version, the firmware version, bootloader version or a combination of all three.
