pylint recommends that every exception class should explicitly
invoke the superclass __init__, even though things seem to work
fine without it.
Signed-off-by: NEric Blake <eblake@redhat.com>
Message-Id: <1443565276-4535-4-git-send-email-eblake@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>