ShardServerOpObserver uses `isStandaloneOrPrimary` to identify if the observed write was done by this node itself (i.e. primary) or from secondary oplog application.

However, the implementation of `isStandaloneOrPrimary` is flawed: It uses ReplicationCoordinator::getMemberState, which turns RS_PRIMARY as soon as the node wins the election. However, the newly-elected node may still be draining oplog. In that situation, the observer should still behave in "secondary" mode.

The correct way to implement `isStandaloneOrPrimary` is to use ReplicationCoordinator::canAcceptWritesFor (which other op_observers already use). `canAcceptWritesFor` will only turn true after oplog has been drained.