Modified policy and tests to verify this change.
As per this change, user with 'creator' role can delete a secret or
a container as long as that user has initially created that secret
or container.
There is still a difference between 'admin' role and 'creator' role
behavior around delete operation. With this change, users with 'creator'
role cannot delete any other user's secret/container in same project
while user with 'admin' role can do that.
Updated role docs to reflect this behavior.
Change-Id: I53e5529ed34ac4acc76348ca0431cb3de7934b6d