Install documentation/makefile out of date

[groob]

I completed a simian install to AppEngine today and ran into several issues that require updates or fixes:

• The AppEngine instructions are not matching the documentation for installing python apps with gcloud.
  The steps described here require downloading a legacy launcher. AppEngine now is part of the gcloud app subcommand.

• custom domains
  If you're using a custom domain with app-engine, the project ID is not the subdomain.
  I had to modify src/simian/util/appid_generator.py because it was combining the project ID with a domain part, but the app.yml should match the following:

application: your-gcp-project-id

For reference, I use acme-corp as the Project ID, but my simian install is served from munki.corp.acme.co.