Is it possible to disable default /vagrant synced folder?
According to source code - it's not, but what if I'm wrong?
So the final question: is it possible to run a vagrant VM (virtualbox-driven) without /vagrant synced folder?
Yes. In the Vagrantfile:
Vagrant.configure('2') do |config|
config.vm.synced_folder '.', '/vagrant', disabled: true
# ...
end