Full support for Keystone LDAP integration

Adding full support for integrating Keystone via LDAP. Enables
support for managing all LDAP related Keystone options.

 - Add two examples of LDAP configuration, although LDAP environments
   are highly variable, these will help get everyone started
 - Modify the keystone::ldap class to support all LDAP related options
 - Check sane defaults in the keystone::ldap class to hopefully reduce mistakes
 - Add a dependency on the python-ldap package
 - Modify the LDAP test to match the new class
 - Make the default-tenant optional since some LDAP backends do not
   support this

Change-Id: Ie6879eb4816fd2b906f72cac8deb3b62bd4b2430
Merge "Full support for Keystone LDAP integration"