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()

Change-Id: Ieb69be9740653645b8e000574ad3fe59a0f97540
Merge branch 'config-local' into dt-test
Merge branch 'hypervisor-xenserver' into dt-test
Merge branch 'ldap-ad' into dt-test