Replace mock with self.override_config
Replace mock with self.override_config

Changing config parameters by one test can lead to wrong behavior
other tests in race conditions. Use a mechanism for overwriting
config options (self.flags and self.override_config methods of TestCase).
This patch allows to use a standard approach.

Change-Id: I4d3200dbaf3ffcd76a04caaec1b9ee166169d6f1

ge0rgi/cinder,eharney/cinder,cloudbase/cinder,Datera/cinder,Hybrid-Cloud/cinder,Datera/cinder,j-griffith/cinder,Nexenta/cinder,bswartz/cinder,mahak/cinder,phenoxim/cinder,NetApp/cinder,openstack/cinder,NetApp/cinder,eharney/cinder,openstack/cinder,Nexenta/cinder,j-griffith/cinder,cloudbase/cinder,mahak/cinder,bswartz/cinder,phenoxim/cinder,Hybrid-Cloud/cinder