3842a1f710
When provisioning multiple machines in sequence (the default vagrant behaviour), it doesn't make sense to require to provide the private ssh key(s) via the custom ansible inventory script/file. To align with the handling of multiple ssh keys per machine, we won't rely any longer on `--private-key` command line argument, but only pass the keys via `ANSIBLE_SSH_ARGS` environment variable. Note that when vagrant generates the ansible inventory and that only one key is associated to a VM, this step would be redundant, and therefore won't be applied. This change fixes the breaking change introduced by 3d62a91.
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.