ATMO-273 Standardize failure responses for the API.

* Fix some identity_membership API endpoints.
* Add failure_response.
* Remove failureJSON.

	modified:   api/__init__.py
	modified:   api/identity_membership.py
	modified:   api/instance.py
	modified:   api/machine.py
	modified:   api/meta.py
	modified:   api/notification.py
	modified:   api/occupancy.py
	modified:   api/provider.py
	modified:   api/step.py
	modified:   api/volume.py
Merge branch 'atmo-273' into gunnr