Suitable grub update method

[gesangtome]

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Use UEFI to start, the default grub.cfg is in '/boot/efi/efi/$ID/',
add a judgment to select the appropriate update method.
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This modification applies to redhat and it's modified version.
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Signed-off-by: 弱弱的胖橘猫丷 gesangtome@foxmail.com

[shvchk]

Thank you, @gesangtome !