Fix API version test to not assume dns endpoint

The test_list_enabled_api_versions test was assuming the location of
the dns endpoint, but in some deployment that assumption is not true.
For example, if designate is using a specific port for the endpoint.

This patch corrects the test to use the keystone catalog to find the
proper designate API endpoint.

Change-Id: Ica672983214774d3ba38391d5fca6d42691f8e2a
diff --git a/designate_tempest_plugin/tests/api/v2/test_enabled_api_version.py b/designate_tempest_plugin/tests/api/v2/test_enabled_api_version.py
index db98a9d..c5fcd69 100644
--- a/designate_tempest_plugin/tests/api/v2/test_enabled_api_version.py
+++ b/designate_tempest_plugin/tests/api/v2/test_enabled_api_version.py
@@ -51,8 +51,8 @@
                 versions = self.primary_client.list_enabled_api_versions()[1][
                     'versions']['values']
             if user == 'not_auth_user':
-                uri = CONF.identity.uri.split('identity')[0] + 'dns'
-                response = requests.get(uri, verify=False)
+                response = requests.get(self.primary_client.base_url,
+                                        verify=False)
                 headers = {
                     k.lower(): v.lower() for k, v in response.headers.items()}
                 versions = self.deserialize(