Fix list_group_snapshots API in v3 group_snapshots_client

The API (list group snapshots with details) is wrongly implemented now.
It uses the '?detail=True' to get group snapshots list with details,
which only returns 'id' and 'name' elements of group snapshots.

This patch fixes on group snapshots api and according api/unit tests to
solve this problem.

Closes-bug: #1715786
Change-Id: Ia869a7dc9654a6253c2209724afd2fe2f8519558
4 files changed