Recordset scenario test suite changes

1) Re-factoring: replace underscores by index, use constants
2) Moving "test_create_soa_record_not_permitted" from Scenario to API
3) New test: "test_delete_ns_record_not_permitted"
   Primary user is not able to delete NS type recordset
4) New test: "test_update_records_propagated_to_backends"
   Update recordset TTL (all types except NS and SOA) and
   make sure that the updated TTL is propagated to the backends
5) Adding backend validation check to the existing test:
   "test_create_and_delete_records_on_existing_zone"
6) Remove "NS" type record from "recordset_data.json"
   Reason: the test was bogus because it was creating an NS record
   for a sub-zone

Change-Id: I169b3666a941ac61ac56619cdbe0f947340f669f
diff --git a/designate_tempest_plugin/tests/base.py b/designate_tempest_plugin/tests/base.py
index 091c3ca..d5cdb6b 100644
--- a/designate_tempest_plugin/tests/base.py
+++ b/designate_tempest_plugin/tests/base.py
@@ -177,6 +177,7 @@
     """Base class for DNS V2 API tests."""
 
     all_projects_header = {'X-Auth-All-Projects': True}
+    managed_records = {'x-designate-edit-managed-records': True}
 
     @classmethod
     def skip_checks(cls):