Householder has a hard dependency on VirtualBox, but it
should not have to depend on vagrant.

Removes all references to Vagrant.

Add instructions on how to test Householder.

document .env.sample

a local variable would suffice

add box-ip to the help text

add comment for BOX_NAME

Always download the box for now to avoid certain types of errors.

Prints status messages, including the VM's name given by VirtualBox.

This helps in reducing confusion when debugging.

Removes `create_nat_adapter`, which causes the process to stall.

For now, let's assume that the base box is setup with a SSH tunnel
at port `7222`.

Pass guest box's username and password, so that we don't make any
assumptions as to what username and password is configured.