Add detail specific fields check in list_backups

Now list_backups is called twice and both with
detail=True and without specific fields check.
This is to:
1. add detail specific fields check when detail=True
2. make one calling of list_backups to use detail=False

Change-Id: Iafbcc2b3048f5fcf1e453da0e4821268ffa0be59
diff --git a/tempest/api/volume/admin/test_volumes_backup.py b/tempest/api/volume/admin/test_volumes_backup.py
index afc3281..375aacb 100644
--- a/tempest/api/volume/admin/test_volumes_backup.py
+++ b/tempest/api/volume/admin/test_volumes_backup.py
@@ -99,8 +99,7 @@
                                                 'available')
 
         # Verify Import Backup
-        backups = self.admin_backups_client.list_backups(
-            detail=True)['backups']
+        backups = self.admin_backups_client.list_backups()['backups']
         self.assertIn(new_id, [b['id'] for b in backups])
 
         # Restore backup
diff --git a/tempest/api/volume/test_volumes_backup.py b/tempest/api/volume/test_volumes_backup.py
index 1f91db6..e45a056 100644
--- a/tempest/api/volume/test_volumes_backup.py
+++ b/tempest/api/volume/test_volumes_backup.py
@@ -83,6 +83,9 @@
         # Get all backups with detail
         backups = self.backups_client.list_backups(
             detail=True)['backups']
+        for backup_info in backups:
+            self.assertIn('created_at', backup_info)
+            self.assertIn('links', backup_info)
         self.assertIn((backup['name'], backup['id']),
                       [(m['name'], m['id']) for m in backups])