Vagrantfile: Avoid extra blocks & shadowing `config` variable
This effectively drops the many Vagrant.configure
blocks and keep only the
main one. Then, it renames the main "config" variable into "cfg" and keep the
local variable "config" for each remaining local vm declaration.
Test Plan
vagrant destroy test; vagrant up test
is fine
Migrated from D4086 (view on Phabricator)