Removed set_loaded() method from Resource class

set_loaded() method should not be available in class public API cause its
usage can break internal class logic. Base Resource class(method __getattr__)
can behave incorrectly if access to attribute _loaded is provided to end users.

method get() of Resource class also should be private, because it's
related to internal class logic and doesn't have any meaning from
outside of the class

blueprint common-client-library-2

Change-Id: I491f9b54c7074546cf738c6150666bfcc3966a78
Merge "Removed set_loaded() method from Resource class"