Only create a TokenClient if api_v2 is enabled

Token clients should only be setup if the corresponding API
version is marked as available. If they are configured as
available but the URI is not set, the configuration is invalid.

Change-Id: Ib2885dbb04af3dc12724fe50bed8ce73ec3c426c
Closes-bug: #1451987
diff --git a/tempest/clients.py b/tempest/clients.py
index a0c9471..9f6a9bb 100644
--- a/tempest/clients.py
+++ b/tempest/clients.py
@@ -22,6 +22,7 @@
 from tempest.common import cred_provider
 from tempest.common import negative_rest_client
 from tempest import config
+from tempest import exceptions
 from tempest import manager
 from tempest.services.baremetal.v1.json.baremetal_client import \
     BaremetalClientJSON
@@ -343,11 +344,22 @@
         self.credentials_client = CredentialsClientJSON(self.auth_provider,
                                                         **params)
         # Token clients do not use the catalog. They only need default_params.
-        self.token_client = TokenClientJSON(CONF.identity.uri,
-                                            **self.default_params)
+        # They read auth_url, so they should only be set if the corresponding
+        # API version is marked as enabled
+        if CONF.identity_feature_enabled.api_v2:
+            if CONF.identity.uri:
+                self.token_client = TokenClientJSON(
+                    CONF.identity.uri, **self.default_params)
+            else:
+                msg = 'Identity v2 API enabled, but no identity.uri set'
+                raise exceptions.InvalidConfiguration(msg)
         if CONF.identity_feature_enabled.api_v3:
-            self.token_v3_client = V3TokenClientJSON(CONF.identity.uri_v3,
-                                                     **self.default_params)
+            if CONF.identity.uri_v3:
+                self.token_v3_client = V3TokenClientJSON(
+                    CONF.identity.uri_v3, **self.default_params)
+            else:
+                msg = 'Identity v3 API enabled, but no identity.uri_v3 set'
+                raise exceptions.InvalidConfiguration(msg)
 
     def _set_volume_clients(self):
         params = {