Adds new scenario test to the Zones suite + minor refactoring

Test name: "test_create_and_update_zone"
   1. Create a Zone using particular TTL and Description values.
   2. Update Zone's TTL and Description.
   3. Make sure that the updated values presents in "Show Zone".

Change-Id: Ic9aa12eb9fd9cdad8f6f765cc98de20b272aaf33
diff --git a/designate_tempest_plugin/common/constants.py b/designate_tempest_plugin/common/constants.py
index 1111c72..57aeab9 100644
--- a/designate_tempest_plugin/common/constants.py
+++ b/designate_tempest_plugin/common/constants.py
@@ -23,7 +23,20 @@
 UP = 'UP'
 CREATE = 'CREATE'
 UPDATE = 'UPDATE'
+NONE = 'NONE'
 
 # Zone types
 PRIMARY_ZONE_TYPE = 'PRIMARY'
 SECONDARY_ZONE_TYPE = 'SECONDARY'
+
+# DNS Record types
+A = 'A'
+AAAA = 'AAAA'
+ALIAS = 'ALIAS'
+CNAME = 'CNAME'
+MX = 'MX'
+NS = 'NS'
+PTR = 'PTR'
+SOA = 'SOA'
+SRV = 'SRV'
+TXT = 'TXT'