CI: Add oslo_db.exception.DBConnectionError to check-logs.sh

Change-Id: Ia1de6d9452e2c900169e9b4ccb7dfc1280283909

tests/check-logs.sh

@@ -35,6 +35,7 @@ function filter_out_expected_critical {
     */neutron-server.log)
         # Sometimes we see this during shutdown (upgrade).
         # See: https://bugs.launchpad.net/neutron/+bug/1863579
+        grep -v "Unhandled error: oslo_db.exception.DBConnectionError" |
         grep -v "WSREP has not yet prepared node for application use" |
         grep -v "Failed to fetch token data from identity server"
         ;;