The code was still dependent on it for the ldap driver.
Changed the driver code to depend on the schema type.
Fix defaults for user and groups trees.
ATM if you use the rfc2307bis schema you have to put users and groups
in 2 separate trees (what people does by default anyway.
If this limitation will turn to be too hard, we will change this later.

The special persistent local database retains the original name.
All other backends now have their own cache-NAME.ldb file.

This patch reduces the time needed to enumerate groups of a midsized
domain from 12 seconds to 4.4
Optimizes enumerations by doing only 2 ldb searches and some ordering
instead of a number of searches proportional to the number of groups

First pass to remove the legacy option and make it just a property of the
provider

If available the original DN and the user principle will be stored
in sysdb.

Also add tests

This uses and exapands the async helpers.