The previous implementation did not handle topology changes well:
* In node_local_only mode with CL=1, if the current node is pending,
the CL is raised to 2, causing unavailable_exception.
* If the current tablet is in write_both_read_old and we read with
node_local_only on the new node, the replica list is empty.
This patch changes node_local_only mode to always use my_host_id as
the replica list. An explicit check ensures the current node is a
replica for the operation; otherwise on_internal_error is called.
ed6bec2cac