Add Tests for Groups Volume APIs - Part 1

This is the 1st patch that adds the tempest tests for generic
volume groups APIs in Cinder. It adds groups and group_types clients.
It tests the following group APIs:

  * create group
  * delete group
  * show group
  * list group

Change-Id: Id1779fe5dce50b062ca0ff841a7ede72cac9dd73
10 files changed