Use apiclient library

This library can be used in novaclient, keystoneclient,
glanceclient, and other client projects. The library
contains common code and uses python-requests for
HTTP communication.

Features:
* share one authentication result between sessions with
  several servers (good for horizon and python-openstackclient);
* reissue authentication request for expired tokens;
* pluggable authentication;
* rich exceptions hierarchy.

Partially implements: blueprint common-client-library

Change-Id: I9155613f012d7372b8a11e0950ac450b31a8c173