Improved MemoizedAuthServiceComposite

 * service property raises an exception if no service is found
 * public_url property raises an exception if not endpoint is found
   in the targeted service.
 * Memoization works correctly for same-credentials/different auth
   systems scenario now.
 * Memoization works correctly when passing instantiated configs
   into the __init__ now.
 * Memoization works for switching credentials by changing the
   configs being used in the same composite now, although this
   isn't recommended.
 * Removed _lazy_property class
 * All properties now properly check the current cached version
   of the access data, instead of caching the first version
   accessed.

Change-Id: I96b720dc6479569dcd9eae793d9993df9bcde00c
Merge "Improved MemoizedAuthServiceComposite"