Don't mark remotes online when shutting down (#11368)

Shutting down will mark remotes online when the shutdown has 
started since the context is canceled.

For example:

```
API: SYSTEM()
Time: 16:21:31 CET 01/28/2021
DeploymentID: 313b0065-c5a1-4aa3-9233-07223e77a730
Error: Storage resources are insufficient for the write operation .minio.sys/tmp/ced455c4-3d27-4bdd-95fc-b4707a179b8a/fd934ef3-8fc8-4330-abc1-f039fbbb9700/part.1 (cmd.InsufficientWriteQuorum)
       1: d:\minio\minio\cmd\data-usage.go:56:cmd.storeDataUsageInBackend()
Exiting on signal: INTERRUPT
Client http://127.0.0.1:9002/minio/lock/v5 online
Client http://127.0.0.1:9002/minio/storage/data/distxl/s2/d3/v24 online
Client http://127.0.0.1:9002/minio/storage/data/distxl/s2/d2/v24 online
Client http://127.0.0.1:9002/minio/storage/data/distxl/s2/d1/v24 online
Client http://127.0.0.1:9002/minio/peer/v12 online
Client http://127.0.0.1:9002/minio/storage/data/distxl/s2/d4/v24 online
```

Use a fresh context for health checks.

cmd/lock-rest-client.go

@@ -161,7 +161,7 @@ func newlockRESTClient(endpoint Endpoint) *lockRESTClient {
 	healthClient := rest.NewClient(serverURL, globalInternodeTransport, newAuthToken)
 	healthClient.ExpectTimeouts = true
 	restClient.HealthCheckFn = func() bool {
-		ctx, cancel := context.WithTimeout(GlobalContext, restClient.HealthCheckTimeout)
+		ctx, cancel := context.WithTimeout(context.Background(), restClient.HealthCheckTimeout)
 		defer cancel()
 		respBody, err := healthClient.Call(ctx, lockRESTMethodHealth, nil, nil, -1)
 		xhttp.DrainBody(respBody)

cmd/peer-rest-client.go

@@ -881,7 +881,7 @@ func newPeerRESTClient(peer *xnet.Host) *peerRESTClient {
 
 	// Construct a new health function.
 	restClient.HealthCheckFn = func() bool {
-		ctx, cancel := context.WithTimeout(GlobalContext, restClient.HealthCheckTimeout)
+		ctx, cancel := context.WithTimeout(context.Background(), restClient.HealthCheckTimeout)
 		defer cancel()
 		respBody, err := healthClient.Call(ctx, peerRESTMethodHealth, nil, nil, -1)
 		xhttp.DrainBody(respBody)

cmd/storage-rest-client.go

@@ -662,7 +662,7 @@ func newStorageRESTClient(endpoint Endpoint, healthcheck bool) *storageRESTClien
 		healthClient := rest.NewClient(serverURL, globalInternodeTransport, newAuthToken)
 		healthClient.ExpectTimeouts = true
 		restClient.HealthCheckFn = func() bool {
-			ctx, cancel := context.WithTimeout(GlobalContext, restClient.HealthCheckTimeout)
+			ctx, cancel := context.WithTimeout(context.Background(), restClient.HealthCheckTimeout)
 			defer cancel()
 			respBody, err := healthClient.Call(ctx, storageRESTMethodHealth, nil, nil, -1)
 			xhttp.DrainBody(respBody)