unit tests: Add a handle_delete method to GenericResource

This allows us to stub it in unit tests.

Change-Id: I9f8ec45e080efb481676be24541a75c16422a765
Unit tests: Don't raise ResourceFailure directly

It's meant to be a wrapper around other exceptions that's invoked by
top-level resource operations; don't use it as an all-purpose exception.

Change-Id: I1e0376a4a00fc3f1114b9bc76bbb1d5d0d98b166
Include the resource and action in ResourceFailure exceptions

An update operation performs 3 different kinds of actions on resources
(update, create and delete), and we may want to handle failures differently
depending on the action.

Change-Id: Icf60a1aea882251150a1507183cf2d23da92675f
Merge "unit tests: Add a handle_delete method to GenericResource"
Merge "Unit tests: Don't raise ResourceFailure directly"
Merge "Include the resource and action in ResourceFailure exceptions"