Associate the correct flatpak installation to each pending app update.

Previously, the flatpak plugin would execute all updates in a single
transaction with the scope (system or user) of the last application in
the update queue. This causes "Update All" to fail when there are
updates pending for both system-wide and per-user flatpaks.

This patch creates a separate transaction for each flatpak
installation and assigns each application in the update queue to the
appropriate transaction.
1 job for wip/hughsie/GsFlatpak in 18 minutes and 52 seconds
Status Job ID Name Coverage
  Build
passed #355078
build-gnome-software

00:18:52