add network read performance collection support. (#8038)

ReST API on /minio/admin/v1/performance?perfType=net[?size=N] 
returns

```
{
  "PEER-1": [
             {
	       "addr": ADDR,
	       "readPerf": DURATION,
	       "error": ERROR,
	     },
	     ...
	   ],
  ...
  ...
  "PEER-N": [
             {
	       "addr": ADDR,
	       "readPerf": DURATION,
	       "error": ERROR,
	     },
	     ...
	   ]
}
```

cmd/peer-rest-client.go

@@ -22,6 +22,7 @@ import (
 	"crypto/tls"
 	"encoding/gob"
 	"io"
+	"math/rand"
 	"net/url"
 	"strconv"
 	"time"
@@ -107,6 +108,37 @@ func (client *peerRESTClient) Close() error {
 // GetLocksResp stores various info from the client for each lock that is requested.
 type GetLocksResp map[string][]lockRequesterInfo
 
+// NetReadPerfInfo - fetch network read performance information for a remote node.
+func (client *peerRESTClient) NetReadPerfInfo(size int64) (info ServerNetReadPerfInfo, err error) {
+	params := make(url.Values)
+	params.Set(peerRESTNetPerfSize, strconv.FormatInt(size, 10))
+	respBody, err := client.call(
+		peerRESTMethodNetReadPerfInfo,
+		params,
+		rand.New(rand.NewSource(time.Now().UnixNano())),
+		size,
+	)
+	if err != nil {
+		return
+	}
+	defer http.DrainBody(respBody)
+	err = gob.NewDecoder(respBody).Decode(&info)
+	return info, err
+}
+
+// CollectNetPerfInfo - collect network performance information of other peers.
+func (client *peerRESTClient) CollectNetPerfInfo(size int64) (info []ServerNetReadPerfInfo, err error) {
+	params := make(url.Values)
+	params.Set(peerRESTNetPerfSize, strconv.FormatInt(size, 10))
+	respBody, err := client.call(peerRESTMethodCollectNetPerfInfo, params, nil, -1)
+	if err != nil {
+		return
+	}
+	defer http.DrainBody(respBody)
+	err = gob.NewDecoder(respBody).Decode(&info)
+	return info, err
+}
+
 // GetLocks - fetch older locks for a remote node.
 func (client *peerRESTClient) GetLocks() (locks GetLocksResp, err error) {
 	respBody, err := client.call(peerRESTMethodGetLocks, nil, nil, -1)