This is needed as we get software instances by their reference and not
their relative urls

slapos_jio_api_style: Add related key to be able to search instance from host compute node reference

* NotFound Errors are now handled by API

Can replace the following SlapTool calls:
* softwareReleaseError
* availableSoftwareRelease
* buildingSoftwareRelease
* destroyedSoftwareRelease

See merge request !696

This will support buildout extension to download from gitlab API with
authentication.

The code has already been refactored a bit to be able to pass a
download instance to SoftwareReleaseSchema, for now to instanciate only
one Download but in the future this might be extended to pass some
configuration to the Download instance.

The performance was much worse.

Workflow state was not the correct one.

See 76edda30