r17330: Enable the partitions module.

r17330: Enable the partitions module.

This module redirects various samdb requests into different modules,
depending on the prefix.  It also makes moving to an LDAP backend
easier, as it is just a different partition backend.

This adds yet another stage to the provision process, as we must setup
the partitions before we setup the magic attributes.

Andrew Bartlett
(This used to be commit 31225b9cb6ef6fcb7bd831043999b1b44ef1b128)