lib/repo-pull: return errors from signature engines
lib/repo-pull: return errors from signature engines

Improve error handling for signatures checks -- passthrough real
reasons from signature engines instead of using common messages.

Signed-off-by: Denis Pynkin <3fbf95ee68899518ee8799d35f88c8f7982aa936@collabora.com>

GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree