[IPC/Client] There's no need to send struct{}{} to notify a

waiting goroutine with an infinite loop about the stop. It's enough
to close stopChan. Moreover it could lead to a deadlock if
driver.Stop is called before driver.handleSubprocessExit.

Signed-off-by: Anton Tiurin <noxiouz@yandex.ru>

storagedriver/ipc/client.go

@@ -158,7 +158,6 @@ func (driver *StorageDriverClient) Stop() error {
 		killErr = driver.subprocess.Process.Kill()
 	}
 	if driver.stopChan != nil {
-		driver.stopChan <- struct{}{}
 		close(driver.stopChan)
 	}