The new TracingReadOnlyTransaction wrapper doesn't do anything
interesting yet - but it will, in the related upcoming next change.
This is one of a serious of (small, easy to review) commits which is
part of a solution I'm proposing in order to be able to detect OOM
issues such as Bug 9034, based on using the mdsal-trace DataBroker.
Change-Id: Ifa82c50d9c9eac76af99bf6a58e5e1955ee7429c
Signed-off-by: Michael Vorburger <vorburger@redhat.com>