Enable assignment sal driver if LDAP is used
Fix for error below. It might be related to LDAP backend. If it enabled `keystone userg-get` doesn't return `tenatnId` row.
err:  (/Stage[main]/Heat::Keystone::Auth/Keystone_user[heat]) Could not evaluate: Could not find colummn tenantId when getting user neutron
err:  (/Stage[main]/Heat::Keystone::Auth/Keystone_user[heat]) /etc/puppet/modules/keystone/lib/puppet/provider/keystone.rb:111:in `get_keystone_object'
Use same password for all service users. Password could be set up via UI
($::fuel_settings['keystone_ldap']['ldap_service_users_pass'])
Switch Keystone LDAP users read only.