[#1652] Fix auth when creating a DataStore resource directly

If you provided a dataset id on datastore_create to create the resource
directly, the auth functions failed as they expected a resource. This
changes the datastore_create auth function to use package_update instead
of resource_update if that is the case.
Merge branch 'master' into 1652-datastore-resources-auth
[#1652] Fix dodgy test
Merge pull request #1652 from ckan/1652-datastore-resources-auth

Creating a DataStore resource with the package_id fails for a normal user