LDAP: Add support for the ldap options

 - Add support for all the ldap related options, but
   ditched default values so that we won't get out of sync
   with keystone
 - Mark the LDAP password as secret
 - Add a package dependency that is required to make
   ldap functional
 - Since defaults are now undefined, define a few basic
   defaults and check them. Also ensure the package dep
   is set