fvp: Prepare the target to be launched via acloud.

- Split the run_model script in two:
  - run_model_only just runs the model;
  - run_model uses run_model_only to run the model and
    automatically telnets to it.
  run_model is what most interactive users want (so it keeps the
  original name) but acloud needs the ability to start the model on
  its own using run_model_only.
- Create a required_images file. This has a similar purpose to
  the required_images file introduced for cuttlefish.

Bug: 156029370
Change-Id: Id70eb3b949802bd3097ba16eabc95de7c4e79d51
4 files changed