Properly watch for users, policies, temp users (#7701)

Users were not reloaded properly when etcd was
configured in gateway, server modes.

This PR fixes this issue.

cmd/config-common.go

@@ -107,7 +107,7 @@ func readConfigEtcd(ctx context.Context, client *etcd.Client, configFile string)
 // watchConfigEtcd - watches for changes on `configFile` on etcd and loads them.
 func watchConfigEtcd(objAPI ObjectLayer, configFile string, loadCfgFn func(ObjectLayer) error) {
 	for {
-		watchCh := globalEtcdClient.Watch(context.Background(), iamConfigPrefix)
+		watchCh := globalEtcdClient.Watch(context.Background(), configFile)
 		select {
 		case <-GlobalServiceDoneCh:
 			return

cmd/iam.go

@@ -79,7 +79,8 @@ func (sys *IAMSys) Init(objAPI ObjectLayer) error {
 			go func() {
 				// Refresh IAMSys with etcd watch.
 				for {
-					watchCh := globalEtcdClient.Watch(context.Background(), iamConfigPrefix)
+					watchCh := globalEtcdClient.Watch(context.Background(),
+						iamConfigPrefix, etcd.WithPrefix())
 					select {
 					case <-GlobalServiceDoneCh:
 						return