Enhance config restore to carry previous set content as well (#8483)

This PR brings support for `history` list to
list in the following agreed format

```
~ mc admin config history list -n 2 myminio
RestoreId: df0ebb1e-69b0-4043-b9dd-ab54508f2897
Date: Mon, 04 Nov 2019 17:27:27 GMT

region name="us-east-1" state="on"
region name="us-east-1" state="on"
region name="us-east-1" state="on"
region name="us-east-1" state="on"

RestoreId: ecc6873a-0ed3-41f9-b03e-a2a1bab48b5f
Date: Mon, 04 Nov 2019 17:28:23 GMT

region name=us-east-1 state=off
```

This PR also moves the help templating and coloring to
fully `mc` side instead than `madmin` API.

cmd/config/config.go

@@ -24,6 +24,7 @@ import (
 	"github.com/minio/minio-go/pkg/set"
 	"github.com/minio/minio/pkg/auth"
 	"github.com/minio/minio/pkg/env"
+	"github.com/minio/minio/pkg/madmin"
 )
 
 // Error config error type
@@ -41,7 +42,7 @@ func (e Error) Error() string {
 
 // Default keys
 const (
-	Default = `_`
+	Default = madmin.Default
 	State   = "state"
 	Comment = "comment"
 
@@ -133,13 +134,13 @@ var SubSystemsSingleTargets = set.CreateStringSet([]string{
 
 // Constant separators
 const (
-	SubSystemSeparator = `:`
-	KvSeparator        = `=`
-	KvSpaceSeparator   = ` `
-	KvComment          = `#`
-	KvNewline          = "\n"
-	KvDoubleQuote      = `"`
-	KvSingleQuote      = `'`
+	SubSystemSeparator = madmin.SubSystemSeparator
+	KvSeparator        = madmin.KvSeparator
+	KvSpaceSeparator   = madmin.KvSpaceSeparator
+	KvComment          = madmin.KvComment
+	KvNewline          = madmin.KvNewline
+	KvDoubleQuote      = madmin.KvDoubleQuote
+	KvSingleQuote      = madmin.KvSingleQuote
 
 	// Env prefix used for all envs in MinIO
 	EnvPrefix        = "MINIO_"