Avoid error modification during IAM migration (#8156)

The underlying errors are important, for IAM
requirements and should wait appropriately at
the caller level, this allows for distributed
setups to run properly and not fail prematurely
during startup.

Also additionally fix the onlineDisk counting

cmd/xl-v1.go

@@ -101,6 +101,7 @@ func getDisksInfo(disks []StorageAPI) (disksInfo []DiskInfo, onlineDisks int, of
 	for _, err := range errs {
 		if err != nil {
 			offlineDisks++
+			continue
 		}
 		onlineDisks++
 	}