Fix to use an API to get the default quota set

Current test_get_default_quotas uses 'os-quota-sets/{tenant_id}'
API.
Now each tenant quota value is tested, but default quata value
has not been tested.

Fixes bug 1167190

Change-Id: I167d430ff923a7c1e54f371ec4b4afe5acca8b1d
Merge "Fix to use an API to get the default quota set"