server: save and compare multiple disks are used (#1474)

When server is run with multiple disks which uses xl interface where
order and count of disks are important, this patch saves such disks
configuration and compares in next run if there is a mismatch.

Fixes #1458

globals.go

@@ -29,12 +29,13 @@ const (
 
 // minio configuration related constants.
 const (
-	globalMinioConfigVersion = "4"
-	globalMinioConfigDir     = ".minio"
-	globalMinioCertsDir      = ".minio/certs"
-	globalMinioCertFile      = "public.crt"
-	globalMinioKeyFile       = "private.key"
-	globalMinioConfigFile    = "config.json"
+	globalMinioConfigVersion    = "4"
+	globalMinioConfigDir        = ".minio"
+	globalMinioCertsDir         = ".minio/certs"
+	globalMinioCertFile         = "public.crt"
+	globalMinioKeyFile          = "private.key"
+	globalMinioConfigFile       = "config.json"
+	globalMinioFormatConfigFile = "format.json"
 )
 
 var (