AbstractConcurrentDataBrokerTest @deprecate-s the AbstractDataBrokerTest

This is take #2 on a similar earlier attempt which made the same change
directly in AbstractDataBrokerTest, which broke some downstrean tests,
which were BADLY WRITTEN (!) because the assumed single threaded direct
execution (which DataBroker does not guarantee).

https://bugs.opendaylight.org/show_bug.cgi?id=7538 has full background

JIRA: MDSAL-556
Change-Id: I05ac3525bdcf1ab9c99dfa15b98e090848d0fddc
Signed-off-by: Michael Vorburger <vorburger@redhat.com>
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit 3282f1989aba438817739bbf611fd133c381a5e7)