We add an error signal to Transaction that the calle (cli) handles. It
decides what to do with the error and whether to continue or abort.
A new error ABORTED is returned from flatpak_run() to indicate
that it errored out because you chose to abort. We also add a new
error SKIPPED that we use to report that some operation is skipped
(due to earlier errors).
This also means we remote the stop_on_first_error argument
from flatpak_transaction_run() as this is now controlled by
the caller.
Alexander Larsson
9b8024326b