Pass identity_version into get_credentials

When identity_version is passed into get_configured_credentials,
pass that into the call to get_credentials as well.

Change-Id: Icfe1efa131518f3190b53b781bfb9b35176eea5d
diff --git a/tempest/common/cred_provider.py b/tempest/common/cred_provider.py
index b0300cb..9630d1c 100644
--- a/tempest/common/cred_provider.py
+++ b/tempest/common/cred_provider.py
@@ -63,7 +63,8 @@
             params[attr] = getattr(_section, prefix + "_" + attr)
     # Build and validate credentials. We are reading configured credentials,
     # so validate them even if fill_in is False
-    credentials = get_credentials(fill_in=fill_in, **params)
+    credentials = get_credentials(fill_in=fill_in,
+                                  identity_version=identity_version, **params)
     if not fill_in:
         if not credentials.is_valid():
             msg = ("The %s credentials are incorrectly set in the config file."