Show volume summary is a new api implemented in volume v3. This patch
is to add a simple test case for this new feature.
Including:
[1] Add v3 volumes_client as library
[2] Add show volume summary api to v3 volumes_client
[3] Add unit tests for show volume summary api
[4] Add test case: test_show_volume_summary
[5] Add release note
Change-Id: I9904bc53896e7d58a22aef11f6a3128147c0a373