Add test coverage for update: SOA and NS managed records

1) "test_admin_updates_soa_and_ns_recordsets"
  Admin uses "x-designate-edit-managed-records" header
  to update SOA and NS records.
  Expected: update request is getting blocked by the API

Change-Id: I4f60dfe62cfae4ffe658fc71d85cd2130054c89f
diff --git a/designate_tempest_plugin/data_utils.py b/designate_tempest_plugin/data_utils.py
index 4b5d24d..4fd47f9 100644
--- a/designate_tempest_plugin/data_utils.py
+++ b/designate_tempest_plugin/data_utils.py
@@ -216,6 +216,19 @@
     return ns_records
 
 
+def rand_soa_records(number_of_records=2):
+    return ['{} {} {} {} {} {}.'.format(
+        '{}.{}.{}'.format(rand_string(3), rand_string(7), rand_string(3)),
+        random.randint(1000000000, 2020080302), random.randint(3000, 7200),
+        random.randint(1000, 3600), random.randint(1000000, 1209600),
+        random.randint(1000, 3600)) for i in range(0, number_of_records)]
+
+
+def rand_soa_recordset(zone_name, **kwargs):
+    return rand_recordset_data(
+        'SOA', zone_name, records=rand_soa_records(), **kwargs)
+
+
 def rand_tld():
     data = {
         "name": rand_zone_name(prefix='tld', suffix='')