Updates to termination point configuration for existing termination points broken

Because TerminationPointCreate/UpdateCommand are keying off creation/update in the config store, not the underlying OVSDB... attempt to create configuration for an existing termination point will result in an attempt to 'insert' an existing interface in ovsdb, which will call the entire transact to fail.

The solution to this is to do a single TerminationPointUpdateCommand in a manner similar to how its done for BridgeUpdateCommand.