Allow user defined roles on non-admin databases to grant permission for users to change their own passwords

Currently the "changeOwnPassword" action needs to be granted to the cluster resource to be effective in allowing a user to change their own password. But roles on non-admin dbs can't have privileges on the cluster resource. Instead, permission to change one's own password should be based on the possession of changeOwnPassword on the database resource for the database the user is defined on.