freshen the LDAP support

* Build the base DN from a given domain name
* Remove all hard-coded names to allow configuration of base DN
* Fix manager DN (cn=Manager,dc=...)
* Add ldap init_ldap()
* Add support for clean.sh

Change-Id: Ieb69be9740653645b8e000574ad3fe59a0f97540
Merge "freshen the LDAP support"
Merge branch 'master' of github.com:openstack-dev/devstack