auth/rpc: Take remote disk offline after maximum allowed attempts. (#3288)

Disks when are offline for a long period of time, we should
ignore the disk after trying Login upto 5 times.

This is to reduce the network chattiness, this also reduces
the overall time spent on `net.Dial`.

Fixes #3286

cmd/posix.go

@@ -18,7 +18,6 @@ package cmd
 
 import (
 	"bytes"
-	"errors"
 	"io"
 	"io/ioutil"
 	"os"
@@ -48,8 +47,6 @@ type posix struct {
 	pool          sync.Pool
 }
 
-var errFaultyDisk = errors.New("Faulty disk")
-
 // checkPathLength - returns error if given path name length more than 255
 func checkPathLength(pathName string) error {
 	// Apple OS X path length is limited to 1016