When embedded-sr option is used, generate a script to supply and request the embedded instance, and call that script after starting the standalone slapos. The instance parameters are stored in a json file and passed via the new --parameters-file option. The user can later call the same script idempotently or edit the parameters.

EDIT: The core of this MR has been merged, what remains now is just:

• Rename the embedded instance from Embedded Instance into embedded_instance and adding a compatibility layer to rename existing instances on the fly.
• Add a test for the compatibility layer.
• Ensure that slapos-standalone-ready-promise waits until the changes are taken into account.
• Some refactoring along the way.