This is required because the Chef Server almost always needs a node name to
interact. This will default to the hostname, but that's always going to be
`vagrant.vm`, which will collide easily.
This generates a random hostname with `vagrant-` as the prefix and stores the
result in the machine's data directory.
Pull up encrypted data bag secret management into the base classes, thus
also unifying the functionality.
Especially this complements the issues:
* Upload the secret to provisioning path also with chef-solo [GH-1246]
* Delete the secret also with chef-client [GH-2712]
* Remove the secret before uploading also with chef-client [GH-1111]