Updated openstack/openstack
Project: openstack/nova  1fc7170b0f82c24e519c4a7e02d138638d3c41d1

xenapi: refactor detach volume

Share more code between detach and detach_all, and make it easier to
read. At the same time, improve the test coverage.

When introducing the new tests, I created a common test base class,
VolumeOpsTestBase that matches VMOpsTestBase.

Change-Id: I7c9d677e7b589b525e2c6ebc43ef81a64a57511d