[SSSD] [sssd PR#186][opened] Subdomain config

[mzidek-rh]

   URL: https://github.com/SSSD/sssd/pull/186
Author: mzidek-rh
 Title: #186: Subdomain config
Action: opened

PR body:
"""
This is the part of subdomain configuration feature needed to allow specify the search
bases for the subdomain (one of the two use cases that were specified in the desin doc).

The second part with the server was more complicated then I expected, so I will send it
separately (hopefully today or tomorrow), but I can not delay this first part anymore).

In order to test create a ipa-ad trust and redefine for example the ldap_search_base or
ldap_user_search_base on the server side SSSD. BOth client and server side SSSDs will be
able to use the alternative search base (no config changes needed on the client side
SSSD).
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/186/head:pr186
git checkout pr186