s4:dsdb Split schema loading and schema data management

s4:dsdb Split schema loading and schema data management

By splitting the module this way, we can load the schema at startup, after
the partitions module is operational, but we leave the 'mess with details of
entries in the partitions' module to operate only on the partitions module.

Loading the schema later allows us to set the @ATTRIBUTES correctly on all
the databases.

Andrew Bartlett