Don't keep parsing command options in gksudo/kdesudo
Don't keep parsing command options in gksudo/kdesudo

When `gksudo` is detected, this module executes the following command:

```
"/usr/bin/gksudo" --preserve-env --sudo-mode --description="MyApp" <COMMAND>
```

Consider the following command:

```
/home/jviotti/Projects/etcher/node_modules/electron-prebuilt/dist/electron /home/jviotti/Projects/etcher/lib/src/run-child-writer.js lib/start.js /home/jviotti/Downloads/CorePlus-current.iso --robot --drive /dev/sdb --unmount --check
```

Given that the command I'm running contains option arguments, it seems
like `gksudo` tries to interpret the options to my command as `gksudo`
options, failing with errors like this one:

```
/usr/bin/gksudo: unrecognized option '--robot'
```

To prevent this from happening, we can tell `gksudo` to stop parsing
options with the `--` identifier.

The same error happens with `kdesudo`.

Signed-off-by: Juan Cruz Viotti <8493db2a4f45d66df375afe12f7eba59fe1c8d78@gmail.com>

jorangreef/sudo-prompt,jorangreef/sudo