Refactor script to be sudoers-friendly

[ExoticMatter]

By extracting the parts of the script that require sudo into a different script, it is (probably) safe to add the extracted script to your sudoers file for use with NOPASSWD.

(Also includes unrelated error handling [if one module fails to load, the rest of the commands will probably fail too; if one can't be unloaded, you can't shut off the GPU])

[lilydjwg]

I have another idea: refactor script so that users are required to run with sudo. Invoking sudo inside will work poorly on exit: it prompts the user to enter password again.

nvidia-xrun.txt

[tangxinfa]

I'm try to fix this problem by rewrite the privilege functions with C:

https://github.com/tangxinfa/nvidia-xrun.git

Implementing details:

The privilege functions use by `nvidia-xrun` was rewrited with C program
`nvidia-xrun-util`, we put the set-user-ID and set-group-ID  bits to the
executable. When executed it will parse the config file
`/etc/default/nvidia-xrun` by itself, then `setuid`/`setgid` to `root` user
for call privilege operations.

So it will not introduce new security problems.

Anyone interesting can try it:

# Build
git clone https://github.com/tangxinfa/nvidia-xrun.git
cd nvidia-xrun
git checkout fix-no-sudo
make permission
# Install by overwrite original nvidia-xrun executable files
sudo ln -sf ./nvidia-xrun /usr/bin/nvidia-xrun
sudo ln -sf ./nvidia-xrun-util /usr/bin/nvidia-xrun-util

If anyone like it i will make a pull request.