Add client's method and test cases for /v2/recordsets API

Partially-Implements: blueprint designate-tempest-plugin

Change-Id: I2d5728d083966aa6b243954bf6cb89d4af473ed7
diff --git a/designate_tempest_plugin/config.py b/designate_tempest_plugin/config.py
index c1dc79f..1a4f2bd 100644
--- a/designate_tempest_plugin/config.py
+++ b/designate_tempest_plugin/config.py
@@ -68,4 +68,7 @@
     cfg.BoolOpt('api_v1_servers',
                 default=False,
                 help="Is the v1 dns servers API enabled."),
+    cfg.BoolOpt('api_v2_root_recordsets',
+                default=False,
+                help="Is the v2 root recordsets API enabled."),
 ]