Load boxes.yaml and allow vagrant-hostmanager to update hypervisor

[ianballou]

Why are you introducing these changes? (Problem description, related links)

What are the changes introduced in this pull request?

• Adds hostmanager config, mainly so that the hypervisor's /etc/hosts is updated along with the VMs' hosts files.
• Increases the dev box disk size to 50 to allow more space for long-lasting logs and Pulp.
• Allows users to create a boxes.yaml file to add to the default box list in the Vagrantfile.

How to test this pull request

Steps to reproduce:

• Try to create a boxes.yaml like

---
# User-local box definitions (this file is gitignored)
# Each entry becomes a vagrant box. Available settings:
#   box:       base box (default: centos/stream9)
#   hostname:  FQDN (default: <name>.example.com)
#   memory:    RAM in MB (default: 2048)
#   cpus:      CPU count (default: 1)
#   disk_size: disk in GB (default: unset)

katello-production:
  memory: 12288
  cpus: 4
  disk_size: 50

• Try vagrant-hostmanager and ensure the hypervisor's hosts file is updated.

Checklist

• Tests added/updated (if applicable)
• Documentation updated (if applicable)

[ianballou]

How do we want to advertise this boxes.yaml file? Docs?

Also this fixes #437

[ehelms]

The failure was due to #497

[ehelms]

Reminds me we should clean up the gitignore as it has some forklift-isms.