[blueprints] Allow defining aliases

[townsend2010]

Make it possible to define and automatically create client-side aliases in the Blueprint definition. It will look similar to:

aliases:
  docker: docker:docker
  docker-compose: docker:docker-compose
  docker-foo: docker-worker:foo

instances:
  docker:
    ...
  docker-worker:
    ...

[townsend2010]

This is related to #2420.