Explicitly prompt user when disabling SELinux using dev-setup script.

The dev-setup script currently disables SELinux for the current running system using `setenforce 0` and also disables it for future restarts by replacing /etc/selinux/config with a file that will keep SELinux disabled.
Disabling SELinux secretly is a bad behavior, so this RFE would add a prompt to the dev-setup script to ask the user's permission to do this.