veyron/services/mgmt/node: addressing limited precision of ModTime().

Change-Id: If056beabe721452e02b52d3c0f156ff523ea45ae
diff --git a/services/mgmt/node/impl/invoker.go b/services/mgmt/node/impl/invoker.go
index 819bf73..bcd0e5a 100644
--- a/services/mgmt/node/impl/invoker.go
+++ b/services/mgmt/node/impl/invoker.go
@@ -522,6 +522,10 @@
 			}
 			return errOperationFailed
 		}
+		// Since the resolution of mtime for files is seconds,
+		// the test sleeps for a second to make sure it can
+		// check whether the "current" symlink is updated.
+		time.Sleep(time.Second)
 		if err := nmClient.Revert(rt.R().NewContext()); err != nil {
 			if err := handle.Clean(); err != nil {
 				vlog.Errorf("Clean() failed: %v", err)