VirtualBox 5.1.6 --- Lubuntu/Ubuntu 16.04 uefi boot issue in virtualbox 5.1.6

When I enable EFI setting in virtualbox 5.1.6 for installing Lubuntu 16.04 x64,

the O.S. after the installation is finished will go into EFI interactive shell, not boot into Grub normally.

How to resolve this problem?
To edit a startup.nsh script manually by using edit startup.nsh command next to add two lines as follows
FS0:
\EFI\ubuntu\grubx64.efi

Press Ctrl+S and Enter to save file and Ctrl+q to quit back to EFI shell.

To reboot OS again, the system will display the EFI shell firstly next to load Grub automatically.