Set default 'ou' name for LDAP projects to Projects

The default ou name for projects/tenants should be Projects, as we normally
use in devstack and ldap live test. Since multiple LDAP objects can
use groupOfNames, setting projects group to Groups is vague.

Fixes Bug1191807

Change-Id: I1718c76320da51a58abf6558a9b8560e908773cb
Merge "Set default 'ou' name for LDAP projects to Projects"
Removing LDAP API Shim

The LDAP identity code had many circular dependecies between
data objects due to the need to look up DNs from ID.   This change
pulls the lookups into the driver layer, and modifies most of the
data objects to take DNs in as their parameters instead. Only objects
that know how to look up their own DNs from thei IDs will continue to
take IDs in, to support the "get" methods.

Change-Id: I0bac360650ccbf72c7ca8317997031420f66e4f3