If a namespace is deleted by another client while we are doing a
namespace list operation, we will fail the list with NotFound if we
try to pull the resource_type_associations list. The latter re-queries
the DB for the namespace and will raise NotFound to us. This is
especially bad because the namespace being deleted need not even
belong to the caller of the list, as is the case in a tempest run.
This makes us catch the failure and continue the operation, reporting
no associations so that the client gets a consistent view and no
error.
Closes-Bug: #1973631
Change-Id: I09fc9164a08f42507d2aec44c5b382a72f232571
35e6c57bc9