init command doesn't work for internal packages

a workaround for now is `npm_config_registry=https://my-internal-registry.com ember-cli-update init -b my-internal-blueprint`

Start by reproducing the `init` command with `my-internal-blueprint`, both with and without the `npm_config_registry` workaround. The issue names no files or tests, so trace the command's internal-package resolution and document completion as successful initialization without requiring the registry override.

Written by the indexing model from the issue text.