config/main: Re-write config files - add to new config v3

- New config format.

```
{
	"version": "3",
	"address": ":9000",
    "backend": {
          "type": "fs",
          "disk": "/path"
    },
	"credential": {
		"accessKey": "WLGDGYAQYIGI833EV05A",
		"secretKey": "BYvgJM101sHngl2uzjXS/OBF/aMxAN06JrJ3qJlF"
	},
	"region": "us-east-1",
	"logger": {
		"file": {
			"enable": false,
			"fileName": "",
			"level": "error"
		},
		"syslog": {
			"enable": false,
			"address": "",
			"level": "debug"
		},
		"console": {
			"enable": true,
			"level": "fatal"
		}
	}
}
```

New command lines in lieu of supporting XL.

Minio initialize filesystem backend.
~~~
$ minio init fs <path>
~~~

Minio initialize XL backend.
~~~
$ minio init xl <url1>...<url16>
~~~

For 'fs' backend it starts the server.
~~~
$ minio server
~~~

For 'xl' backend it waits for servers to join.
~~~
$ minio server
... [PROGRESS BAR] of servers connecting
~~~

Now on other servers execute 'join' and they connect.
~~~
....
minio join <url1> -- from <url2> && minio server
minio join <url1> -- from <url3> && minio server
...
...
minio join <url1> -- from <url16> && minio server
~~~

pkg/fs/fs.go

@@ -1,5 +1,5 @@
 /*
- * Minio Cloud Storage, (C) 2015 Minio, Inc.
+ * Minio Cloud Storage, (C) 2015, 2016 Minio, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -96,7 +96,7 @@ type Multiparts struct {
 }
 
 // New instantiate a new donut
-func New(rootPath string, minFreeDisk int64) (Filesystem, *probe.Error) {
+func New(rootPath string) (Filesystem, *probe.Error) {
 	setFSMultipartsMetadataPath(filepath.Join(rootPath, "$multiparts-session.json"))
 
 	var err *probe.Error
@@ -126,7 +126,7 @@ func New(rootPath string, minFreeDisk int64) (Filesystem, *probe.Error) {
 	/// Defaults
 
 	// minium free disk required for i/o operations to succeed.
-	fs.minFreeDisk = minFreeDisk
+	fs.minFreeDisk = 5
 
 	fs.listObjectMap = make(map[ListObjectParams][]ObjectInfoChannel)
 	fs.listObjectMapMutex = &sync.Mutex{}
@@ -134,3 +134,8 @@ func New(rootPath string, minFreeDisk int64) (Filesystem, *probe.Error) {
 	// Return here.
 	return fs, nil
 }
+
+// GetRootPath - get root path.
+func (fs Filesystem) GetRootPath() string {
+	return fs.path
+}