Fix missing webmin install automation flags

[benjamink]

Adding a couple flags to automatically run commands without prompting for the Webmin easyinstall.sh setup. These additions keep the script from prompting the user to continue:

• Add a -f to the setup-repos.sh script that adds the Webmin package repo
• Add an --assume-yes for installing the webmin package

[rdmark]

I wonder if it's worth also doing </dev/null here to pass an empty input stream to the script and avoid other unexpected prompts? (Due to current or future bugs in a script that's out of our control)

[benjamink]

Not exactly sure what that does. Does that just ensure there aren't any stray characters/commands that get accidentally processed as key clicks when the script runs?

[rdmark]

It establishes an empty stdin stream…. So if the script stops and waits for stdin it will get an empty input and process that accordingly. The actual effect will depend on the script. We could test what happens if the repo hasn’t been added and -f not passed!

[rdmark]

Upon second thought, this is probably a bad idea. :)

If the behavior of the Webmin bootstrap script changes and starts prompting for something new, we probably want to expose that to users.

The </dev/null input stream workaround is more for tools like apt-get which aren’t guaranteed to always behave when running non-interactively — https://stackoverflow.com/questions/54736013/why-does-apt-get-consume-stdin-when-it-installs-something-but-not-otherwise