added vagrant-cachier section to Vagrantfile, it's a no-op if the vagrant-cachier plugin is not installed. If vagrant-cachier is installed then all devstack downloads in the /opt/devstack folder will be cached at the base-box level. This means that even after you tear down your openstack server subsequent vagrant up commands will only have to download the diff between what's in the cache from the last run and the new run. Should dramatically improve startup time.