Having installed schema in one file and schema updates in other file(s) is error prone and causes issues as #3398.

We should instead base updates on the schema files and have the updater validate current DS schema with the LDIF file and amend the schema.

Simo suggested this process:

1. Download schema from server (we already do this in the framework so it comes for free)
2. parse the schema files and check if each attribute and objectclass is present and in the correct form.
3. if any attribute is missing, we add it
4. if any attribute has been changed, we change it
5. same for object classes.

python-ldap's convenience classes can be used to make the comparing easier.