Use error_fatal to simplify obvious fatal errors (again)

Done with the Coccinelle semantic patch from commit 007b0657, plus
manual clean up of dead variables.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1452783732-6581-1-git-send-email-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>