router: drop connection detach in failover

[Serpentian]

Failover automatically detaches connection, when cannot ping replica. This behavior causes more problems, than solves: e.g. on some installations the number of such detached connection is several thousands just because replica is down.

We should find another way of solving the problem of long requests. One of the solutions may be giving user a special API for creating connection, which will be used solely for requests with large return values. But for now we should drop detaching connections.