Adding management_url to test mock client

Mocking management_url property in keystoneclient.Client for mox.

Change-Id: I53dbb9357808584007b2871d4804150e2c547436
Closes-Bug: #1268631
(cherry picked from commit f7d00b5960c4e7f878a647e6c83ead986d55f921)
Merge branch 'stable/grizzly' of https://github.com/openstack/horizon into grizzly/router_rules