A tons of unnecessary read operations in the switch update processing control flow

The performance of the OVSDB Southbound Plugin to process Update Notification from Open vSwitch is really slow. One of reasons of the bad performance is that the plugin does a lot of unnecessary read operations on MD-SAL. The run() method of the TransactionInvokerImpl class calls a lot of the unnecessary read operations. This has a lot of bad impact, especially when we run several OpenDaylight nodes as a cluster in which an OpenDaylight node sometimes needs to communicate with another node (shard leader) to get data during the read operation.

We are thinking this bad performance probably causes the NETVIRT-5 which is a critical bug for NetVirt.
Therefore, we need to fix this problem. Especially, in this bug report, I would like to focus on removing the unnecessary read operations during processing Update Notification.