ovn-controller: No bridge for localnet port is not an error

[Frode Nordahl]

Example log messages:
bridge not found for localnet port 'provnet-9d4a9910-01c3-4fe3-bae3-0d93dc6c9b69' with network name 'physnet1'

Filing here for tracking and for pointing anybody hitting it to the patch.

There is a pattern among CMSes to create a `localnet` port
binding without any chassis affiliation.

It is then up to the user to configure chassis with external
connectivity by adding a mapping under the
`external_ids:ovn-bridge-mappings` key in the Open_vSwitch
table of the local OVS instance. This may be some chassis
or all chassis depending on end user requirements.

At present `ovn-controller` will repeatedly log an error on
chassis without mapping for a localnet port while in reality
it is not an error.

A fix for this was proposed but was NACK'ed:
https://patchwork.ozlabs.org/patch/1245848/

After re-evaluation a different version of essentially the same patch was accepted upstream:
https://patchwork.ozlabs<email address hidden>/

[Frode Nordahl (fnordahl)]

The fix is in 20.06 in Groovy