Separate quota_classes client from quotas client

Each resource should be implemented in each separated module.
quota_classes and quotas are different resources like
  os-quota-class-sets
  os-quota-sets
So this patch separates quota_classes client from quotas client.

Partially implements blueprint consistent-service-method-names

Change-Id: Icd98294c7a161f5c8c1d7202df9f3e6d9daee1d9
diff --git a/tempest/clients.py b/tempest/clients.py
index 9f6a9bb..f0aedd5 100644
--- a/tempest/clients.py
+++ b/tempest/clients.py
@@ -56,7 +56,8 @@
 from tempest.services.compute.json.migrations_client import \
     MigrationsClientJSON
 from tempest.services.compute.json.networks_client import NetworksClientJSON
-from tempest.services.compute.json.quotas_client import QuotaClassesClientJSON
+from tempest.services.compute.json.quota_classes_client import \
+    QuotaClassesClientJSON
 from tempest.services.compute.json.quotas_client import QuotasClientJSON
 from tempest.services.compute.json.security_group_default_rules_client import \
     SecurityGroupDefaultRulesClientJSON