This PR will allow users to pass arguments to he installer and have them be passed to the actual installer.

Example:

$ cat test.sh 
#!/bin/sh
{
echo "$@"
}

$ cat test.sh | sh -s hi eelco
hi eelco

Then, the interior installer can learn --no-daemon and --daemon, forcing on or off the switch to the daemon installer, overriding any detection done. The nix 2.0-maintenance can then receive the patches but default to single-user on Linux, but users can override it.

I'm hoping that by merging this PR and a subsequent PR to Nix we can bring back the multi-user installer for Linux 2.0.