Disable the execution of ``LoggingTestJSON`` in older branches

The OVN logging feature needed for Neutron was implemented in [1].
This patch is provided in v20.12.0.

The unmatained branches running with ML2/OVN in Focal (Ubuntu 20.04),
use the provided OVN package, v20.03, that doesn't have this patch.

[1]https://github.com/ovn-org/ovn/commit/880dca99eaf73db7e783999c29386d03c82093bf

Closes-Bug: #2082066
Change-Id: Id3ecf975516d459358bb5fcd01085ec6a3bdbd26
2 files changed