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/xl-v1.go

@@ -77,6 +77,7 @@ var xlTreeWalkIgnoredErrs = []error{
 	errDiskNotFound,
 	errDiskAccessDenied,
 	errFaultyDisk,
+	errFaultyRemoteDisk,
 }
 
 // newXLObjects - initialize new xl object layer.