Add support for dynamic virtual machine IP addresses

Use the following environmental variables to change the private IP address used by the Vagrant virtual machines:

- `NYC_TREES_APP_IP`
- `NYC_TREES_TILER_IP`
- `NYC_TREES_SERVICES_IP`
For DRYness, consider doing the following:
```ruby
SERVICES_IP = ENV.fetch("NYC_TREES_SERVICES_IP", "33.33.33.30")
ANSIBLE_EXTRA_VARS = {
  redis_host: SERVICES_IP,
  postgresql_host: SERVICES_IP
  ...
}
```