Mark LDAP password and admin_token secret

Add secret=True to LDAP password and admin_token
of keystone configuration.

Fix bug #1172195

Change-Id: I8ef7f705e3f6b374ff427c20eb761892d5146a75
Upstream-Havana: https://review.openstack.org/#/c/26826
Resolves: CVE-2013-2006