[#84] Fix auth audit exception when creating datasets

This was caused by a combination of the auth audit leaking and the
harvester reusing the context for the package_show and package_create
actions. If the package is not found, package_show does not call
check_access, and the auth audit does not pass. This is stored in the
context (`__auth_audit`) and is raised next time that we call
get_action (when we call package_create with the same context)

It could potentially be fixed on master, but it is probably quite rare.