Changes in "test_quotas.py" API script

1) Re-factoring:
   1. Replacing underscores by indexes
   2. Moving all negative tests into the dedicated class
   3. Using all_projects_header
2) Changing "test_show_quotas" test logic.
   The existing test is based and depends on "quotas update" API
   and it has almost the same logic as:"test_update_quotas".
   New scenario is about to validate that all expected quota types
   are listed in "Show API" response and that their values are integers.
   Note: test uses both: admin and primary users to cover both "show" APIs:
   https://docs.openstack.org/api-ref/dns/?expanded=get-the-name-servers-
   for-a-zone-detail#view-quotas
   https://docs.openstack.org/api-ref/dns/?expanded=get-the-name-servers-
   for-a-zone-detail#view-current-project-s-quotas
3) "test_admin_sets_not_existing_quota_type" - try to set quotas using
    not existing quota type in its body, expected: quota_resource_unknown

Change-Id: I9b3d6ee5fc27011b8852739f0ca3ab33fd04d58e
2 files changed