Stabilizing “PTR record” tests suite and adding new test cases

Stabilizing
1) The same TLD is used by default for all tests
2) Adding waiters for set/unset PTR records
New test cases
1) test_show_floatingip_ptr_impersonate_another_project
2) test_list_floatingip_ptr_all_projects
3) test_set_floatingip_ptr_not_existing_fip_id
4) test_set_floatingip_ptr_huge_size_description
5) test_set_floatingip_ptr_invalid_name

Note:
This tests also includes refactoring of the existing tests.
Negative logic is now removed from positive test cases and
implemented separatly in DesignatePtrRecordNegative class.

Change-Id: I64483c3d8e1ae44db7712b3e463ae4ea239a613a
diff --git a/designate_tempest_plugin/common/constants.py b/designate_tempest_plugin/common/constants.py
index 84ee5ae..4f6c72b 100644
--- a/designate_tempest_plugin/common/constants.py
+++ b/designate_tempest_plugin/common/constants.py
@@ -19,6 +19,7 @@
 DELETED = 'DELETED'
 ACTIVE = 'ACTIVE'
 UP = 'UP'
+CREATE = 'CREATE'
 
 # Zone types
 PRIMARY_ZONE_TYPE = 'PRIMARY'