cpu: fix ticker to avoid close early

Signed-off-by: Weizhen Wang <[email protected]>

util/cpu/cpu_test.go

@@ -43,7 +43,7 @@ func TestCPUValue(t *testing.T) {
 		}()
 	}
 	Observer.Start()
-	time.Sleep(30 * time.Second)
+	time.Sleep(5 * time.Second)
 	require.GreaterOrEqual(t, GetCPUUsage(), 0.0)
 	require.Less(t, GetCPUUsage(), 1.0)
 	Observer.Stop()