Specifically, the "privileged" attribute, which in your Vagrantfile, is not set, and therefore defaulted to "true":
privileged (boolean) - Specifies whether to execute the shell script as a privileged user or not (sudo). By default this is "true".
And to be absolutely certain, you can add "whoami >> whoami.log" anywhere inside your install.sh script, and you can see it is "root". This is likely how you're already able to modify your config files without sudo.
And thanks Jeffrey for all that you do... I'm a big fan. :)
Vagrant is already running install.sh as root, so the "sudo"s inside of it are unnecessary.
See:
http://docs.vagrantup.com/v2/provisioning/shell.html
Specifically, the "privileged" attribute, which in your Vagrantfile, is not set, and therefore defaulted to "true":
And to be absolutely certain, you can add "whoami >> whoami.log" anywhere inside your install.sh script, and you can see it is "root". This is likely how you're already able to modify your config files without sudo.
And thanks Jeffrey for all that you do... I'm a big fan. :)