Enhance V3 router class for resources

RESTful APIs are resource-oriented, and Keystone provides a
RESTful API, but the current way that routes are being mapped is
based on URLs rather than resources. With this change, the base
Routers class is enhanced to support a resource-oriented way to
map paths to controllers and methods.

bp json-home

Change-Id: I0ba856845116b3ddd3dfed4608be65a87d9c01dc
Merge "Enhance V3 router class for resources"