Previously vminsert could write multiple copies of the data to a single vmstorage node when the ingestion rate
exceeds the maximum throughput for connections to vmstorage nodes.
Previously the ingestion performance has been limited by the slowest vmstorage node.
Now vminsert should re-route data from the slowest vmstorage node to the remaining nodes.
* Spread load evenly among remaining healthy nodes instead of hammering
the next node after the unhealthy node.
* Make sure that the packet is flushed to storage node before returning success.
Previously packets could stay in local buffers and thus lost on connection errors.
* Keep rows in the limited memory when all the storage nodes are unhealthy.
