* NotFound Errors are now handled by API

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

See merge request nexedi/slapos.core!455

See merge request !478

See merge request !495

This is no longer guessed on Zope4

this way we can just assert the full page content